Unless you're already fairly fast, and you get a racing-style 'bent, you probably won't see a speed increase on one. The reason being, you have to be traveling at >16 or 18 mph to get any aero benefit, and an entry-level bent isn't going to have light weight and aerodynamics going for it in the first place. If you just want to try recumbents, I suggest looking for a RANS Rocket. You should be able to find one for $600-800 with a minimum of searching.