I'd definitely go with a Ride Agenda over going to some crap brands (5150, lamar, etc) but you get what you pay for. The most I could say about it is that it's a solid board. I'd take a look at the K2 Raygun though. It'd probably be able 350$ but it's a cheap board that you kind of forget is a cheap board.
Will the agenda's slightly lower quality be noticeable to someone new like me and will it be durable enough to last me a 2 years or so?
I started up on a completely dried out, too short, 5 year old santa cruz board when I started. Didn't know any better until I was better. If it only has to last 2 years then it probably doesn't matter what you get. If you're only an occasional rider you'll only probably crave a better board in about that time frame anyways. Oh and anything from 150-155 should be fine, size wise.