For $50 and under I like this one... Five settings to control amount of injection per trigger pull. I also have the cheaper plastic ones like the Cajun Injector etc. and they are good too.
I got this one from www.alliedkenco.com but several other places sell them under different brand names.
I have this one, it is a medical grade syringe for horses, but all the normal injector needles fit it. You can dial what amount just like Vinny's and its $11.98 at Tractor Supply.
Try Spitjack.com , the guy that owns it is a big BBQ Nut, his company makes the one that is in Vinnies post, its $49.00 but somtimes its on sale for $42.00. it the the most reliable injector out there today. If youask he has given me extra needles in the past but have never had to use them
I ordered the one from TSC for 12.95. I figure it's an upgrade from the Wal-Mart cheapies I've been using (and replacing). If this one doesn't hold up for me, I'll splurge on the Spitjack one.