Here's what a commercial starter package looks like... Pro Star Sports Field Operators Starter Packages.
Tippmanns are more expensive than stbb's, but the stbb's require twice as much maintenance. Of course, the stbb's take half as long as a tippy to maintain, for an experienced guy. The cost ends up being about the same, when it comes to cheap stbbs.
Something I've wondered, though... The number one problem with field rental stbb's that I've seen is that the sears and the hammers wear out. Most field rental stbb's are piranhas. Meanwhile, Spyders have hardened hammers and hardened sears... That's a HUGE decrease in replacement parts. The most common wear part after the hammer/sear is the detent, and then the trigger sear, which may or may not be hardened on spyders.
You can probably find an adequate fleet of either Tippmanns or Spyders for under that 500 dollar investment point... But it might take a bit of time to get them together.
I know Melkson was looking at selling some stbbs, but I'm not sure which brand. And since Spyders are the only ones that I know have hardened components, I would stick to them.