I checked out the links to the Eheims that Erin plans to purchase. Geesh! $350 for a filter! What is the advantage of using an Eheim over a Marineland 350?
Eheims have an unmatched reputation for quietness and quality workmanship. An Eheim filter can last a liftetime with proper maintenance.
If you want a cheaper alternative try a RENA Filstar canister filter. The XP1 model should be fine for your 30 gallon tank and it's well under $100.00.
I am an Eheim addict. Most of my externals operating are the old Classic series, so less user-friendly than the Pro series, but they are also mostly 20+ years old. In life cycle costs, I think they are by a wide margin the cheapest filters on the market.