If your on a small budget my advice is to not get in a hurry. You should consider checking craigslist, or other used sites that might be more local to your area. You can often pick up a 50 gallon aquarium on the cheap, and have a few pieces of glass cut by a shop for $30 bucks. If your not into DIY projects, then check those sites out for exactly what you need.
A new 50 gallon sump/refuge is going to cost $250 bucks plus shipping from a company I've used in the past.