I don't think anyone would consider you are being cheap, on the contrary it's a nice generous gesture. But I think there are two distinct areas here. First are the top 1% of Pattaya boys and a large proportion of Twilight Agogo boys, for whom a better off is a realistic prospect. Then there is the other 99% of Pattaya boys and all host bar boys where unless they are in huge demand a better offer on any particular night is unlikely. I'm not sure what category your boys are in, if they are superstars and in great demand I wouldn't consider without discussing upfront and making an acceptable offer, whatever category they are in I agree with cdnmatt and Dodger in that Bt500 is fair.
I totally disagree with those who have suggested the tip for a sexual and non-sexual liason should be the same, that's absurd especially in Pattaya where the amount of boys who can command top dollar on a nightly basis is very rare. It's all down to circumstances as following experiences show. One of the boys I talk about below even did have the prospect of an off in the sunee host bar he works and he is an attractive lad, but he said he really didn't like the potential customer who had opened a bottle of whisky and all the lads in the bar were sharing. Also the potential customer had not given any assurances so he was happy for the chance to be elsewhere.
I sometimes/often off boys for a night of sanuk or non-sexual fun. I'm just back from my most recent trip so have some limited recent experiences. My visit could still be considered 'busy' season and in Pattaya had offers from boys only to pay off fee for going for a night of sanuk (and even sex) with no tip required. I took off 3 boys from Pattaya bars for sanuk evenings/nights, of course I offered and gave Bt500 tips to all, one said a tip wasn't necessary as I had paid off and he enjoyed the night with free drinks and food, of course he did accept it. The other two just accepted the Bt500 when offered at the end of the night and seemed delighted, all suggested repeats.
All liaisons basically came about when chatting generally in the bar and them asking what my plans for the evening were, I said visiting a couple of bars in North Pattaya where my Thai friends work in rock bands or Walking St or clubs/music bars and whatever and on each occasion it was they who offered to accompany me, [pbai duay!] "only pay bar, no tip ok!" Some of the lads know I have a bf and that he doesn't like the bars every single night, whereas I do, it's an essential part of my holiday! As is usual a couple of the Duks bar and Eden bar lads even offered to 'thrown in' sex if I wanted. But as Dodger experiences I find many of the lads working in the bars love a night of fun and some really enjoy the noisy music bar/club environments and likewise with Dodger give Bt500 at end of evening/night and all pleased with arrangement.
I also had a similar night with a lad who works in Silom Soi 4, I hadn't seen him for a while and he had been working Soi 4 for a few months and again it was he who offered to accompany me. He was able to get off a bit early so we went to DJ Station which closed suddenly and early at 2am! so we headed to GOD where I haven't been for ages, and it was good vibe there compared to previous visits some time ago. Had great time, he said it was rare to get a night out and was chuffed with Bt500 for taxi home, in fact he seriously said it wasn't necessary. accepted it for old times sake...haha. I had a great time too so it was win-win. I wasn't looking for anyone in DJ or GOD so it was handy to already be with someone to avoid potentially awkward approaches.
Also a counter arguement to Fountainhall's denying the boy income, for the vast majority of working boys realistically an off every night just doesn't happen so bucknaway, dodger may be offering the only prospect of income for that night, Bt500 is still better than zero.