You can get Eheim 2217s from Drs. Foster & Smith for $130 each, and they come with media. Personally, I LOVE my 2217 and I think two should cut it on a 150 gallon.
I don't see an FX5 under $235 on ebay, and Iffrat says another $100 for media, so I'll go with his number on that- that brings you up to $335. For $335 you could get two 2217s and still have $75 left over for whatever you wanted- a couple powerheads, a large HOB for some mechanical filtration & water movement(Aqua Clear is around $80, Emperor 400 is $50), or even a third small canister- Rena & Eheim canisters are both available for $75. My personal opinion of every Fluval product I've ever seen is that the engineering behind them doesn't compare to the simplicity of an Eheim Classic, but, that's my opinion. I've also never actually seen an FX5 in person, only pics online, so I could possibly be swayed. I doubt it, though. . . For me, there's no question- if I could buy three Eheims for the price of one FX5, I'd go for it. If I could only get two 2217s and that's it compared to one FX5, I'd still go with the Eheims.