Never directly offered money to a straight guy for sex, but have used it as a "tool" to help get what I might not have gotten otherwise. Based on my own two "money" experiences - I think if you get the right guy in the right conditions and under the right circumstances, you can probably offer or use money to ease things into motion if you had to -- you might have to pay out to get what you want or you might just get what you want without any money involved. It could work either way.
I think you're right - most "straight" dudes today, who are our age, are pretty easy going as far as sex goes. They're just sexual beings,and don't really care who's on the end of their cock as long as it feels good and they get a nut. Most of them are aren't gonna go out looking for dudes to bang or suck their cock, but sure, a percentage of them would easily say yes (and do) to a good blowjob from another dude. But yeah, a guy who is mostly willing to let you suck his cock already, would have no problems letting you do it for a hundred bucks. No dude in his right mind is going to turn down a good nut and a 100 bucks cash in today's economy, right?!!! lol
I don't think though that I would just walk up to total strangers and tell them you'd pay them to suck their cock or whatever -- you might get the shit beat out of you, or even worse, in some places, get yourself killed.
My two money stories -
First time - Cute guy at gas station asking for cash to get gas to go wherever, blah blah blah. I told him I'd pay for his gas, but not give him cash. Not what he wanted to hear. So the story changed to some other reason for cash. I told him no. He was like "Whatever dude" and was about to walk off and I told him if he showed me his dick I'd give him 5 cash. He said make it ten. I said nah, 5 is all. I drove my car to the side of the car wash and he walked over and pulled it out right there at driver side window. Nice cock too! Thick and cut, looked like it probably had the ability to get a lot bigger. I had the $5 out, started to hand it to him and pulled it back and told him if he wanted 10, I wanted to get him hard with my hand. He shook his head and said nah, a dude's not touching my junk, not into that. I gave him his 5 and he walked away. Still couldn't believe I had done it. Don't know what made me, not something I would really ever do, but the moment just struck me so I went with it. It was pretty cool though, I got to see a good looking straight dude's cock in my face, and he walked away with the cash he had originally wanted, but just not for free, he had to give up something to get it. Not his intention, so in the end I felt like I won on that one.
Second time - Guy I was working with on a residential construction job, pretty sexy, turned out he and my boyfriend were actual friends from way back. I was telling my guy that I thought this guy was hot, and what I'd like to do with him, but that he was way straight and I was pretty sure it wouldn't happen. My guy smiled and said "Don't be so sure, yeah he's straight, but he's broke as fuck - wave a 20 under his nose and see how fast his pants come off." I asked my guy if he and this dude had ever hooked up, and he said no, but he knew the guy was a horndog and would do just about anything as long as he got sucked or got to stick his dick in a warm hole.
Next time after we knocked off work I asked the guy if he wanted to go have some brews, he was up for that. We headed back to his place. I stopped and bought two sixes. We were just drinking and talking. I told him I was close friends with Adam (my guy) and he said OH YEAH, I KNOW HIM! and then he looked at me and cocked his head back and asked me if I was gay. I told him I was bi, but I was more into dudes at the time. He then asked me if I was there with him thinking we were going to have sex. I told him no, I was there to drink beer but if sex happened, that'd be OK. He told me he wasn't gay. I told him neither was I.
I just asked him outright if he'd do anything sexual with a dude as long as there was no touching or kissing or anything. He asked me like what? Told him like gettin naked and jacking off while another guy watched. He laughed at me and said no way, because he couldn't get hard for another dude. That was when I threw in the cash factor and asked him how about for maybe 50 bucks? He thought about it and was like yeah, what the fuck? He'd do it if he could. Guy got naked in front of me, fucking HOT body, big cock, and sitting there on his couch with his eyes closed he started jerking off..... didn't take him long at all, maybe 5 minutes and he shot a huge load of cum all over his stomach and chest. DAMN it was hot!
He asked me if I was impressed and I told him Oh hell yeah, I was more than impressed and pointed to my own jean covered hard-on. He was like "I did that to you?" I said oh yeah, you sure as hell did. Here's the kicker though -- He waited a couple of minutes and then said Ya know, I think it'd be kind of interesting to see another guy jerk off in person...... if you wanna do it I'd like to watch and it'd be cool with me, I've never seen another guy come in real life. Fuck me! Didn't have to ask me twice. I got out of my pants and shirt and was shooting my load on his coffee table in about two minutes! We laughed about it after it was over, he said it was pretty cool to see and he could maybe do it again sometime. We were OK after that, drank more beer and I finally went home. He never asked for the money....!
Next day at work was a little awkward, but we were fine with each other on that job until it finished. Nothing was ever said by him or me. I've never seen him since then.
So - see, it depends. Money can help, like a dog treat needed for that extra little bit of coaxing. Or maybe just two or three beers and some relaxed conversation. But just remember, if a dude is truly straight and has no interest in sex with you or any other guy, and he tells you that, you can ask him again, but if he says no and you can tell he truly means it, let it go. Respect him on that level and move on.