I don't know how it is in other countries, but here in the United States, if you don't tip bartenders, don't expect good service.
Especially when crowded, you will be fucking ignored and only served when the bartender is goddamned good and ready and after taking care of everyone else that came in the line after you too.
Drop some extra dough, it won't kill you and the guys behind the bar might even buy you one or more drinks as the night progresses.
Often after styling the bartender out, he (or even better she) will also bypass other people who have been waiting longer than you have in crowded situations to get your drink (which by now he/she has memorized, money makes people do stuff like that.)
There have been more occasions than I can count where I have walked into a spot days/weeks/months after taking good care of the help previously and the peeps behind the bar recognize you and they're like BOOM, first one's on me. Depends of course on the place, but it almost always pays to tip and tip good.
Then again I work in the service industry and it's just second nature to take care of people whose living is made off of tips.
As far as if you're scrimping and on a budget, why the fuck are you out at a bar or club drinking anyway?
You obviously can't afford to go out and you would be better off copping forties from the corner store.