hey!,
I know I let this go a little dead, but it sounds like you may still be in need of a solution. Hopefully I'm not too late!
Projectors for live events (IMAG) get expensive fast, and its important to balance brightness, lens ratio, resolution and thermal/noise performance, but generally speaking when you're trying to go cheaper its a good idea to start by finding the brightest projector you can and adding features from there. I would not recommend anything less than a 3000 lumen projector for typical gym use, just based on what I've seen at FRC events, you'll need more lumens if you have an exceptionally large throws or screens, or may be able to get away with less in smaller/tighter situations. If you can afford it, a bi-lamp projector will give you the flexibility to use only one lamp in darker rooms or with smaller screens, or use both bulbs when a brighter image is needed. many can also automatically switch over to the second bulb if the first fails in single bulb mode.
If you have the purchasing power necessary, 3300-5000lumen Christie brand projectors with medium pc resolutions (think XVGA - SXVGA, plenty good for IMAG) pop up on ebay frequently for less than $700, and often times include a hard case or "roadie case." be wary of bulb time, as replacement bulbs often also run up to the $300-500 range, but you should be able to find one with a brand new bulb, or not too many bulb hours on it.
If you have to buy from a district or corporate vendor, some that I have used in my school district are B&H Photo Video, Tech Depot, and a few local Houston vendors. A local vendor with an agreement with the local school district can likely get you a good price on a higher end epson model. Benq projectors are affordably priced, and should be considered, but avoided if possible, I don't like there menus and they've always just seemed a little more finicky to me.
A good tool for evaluating a projector you might purpose is the calculator available for free at
http://www.projectorcentral.com/projection-calculator-pro.cfm
Hope this helps you, or someone else if you've already made your purchase