Some things to consider on the tent rent/buy:
How often do you expect to convene a tent - once a year at just this event?
How are you transporting your kit - I have a Suburban with a box on top and I fill it full - so will you have room for the tent?
How much do you want to customize your kit - if you are renting tents you don't always know the set up or how you will hang your displays etc. If you have your own tent you can set things up the way to want knowing the next time will be the same.
Tents like an e-z up or similar will run you more that $50 but will last longer and stand up to the weather better. But beware; your enemy isn't rain it is wind so always tie down your tent as securely as possible and be ready for the worst.