The key thing to watch with Lipos is the discharge or "C" rating. If you pull more current from a pack than it can handle, you could damage it and you will shorten it's lifespan. In many cases, what you get for the extra cash is an ability to handle higher current, better pack assembly, and better quality control.

So, do a back of the envelope calculation and figure out how much current (roughly here) you might pull. If it's low enough, then you've nothing to worry about.

Some battery brands rate their packs higher than they really should. There's no standard on how you measure and rate packs when it comes to discharge current. You might find the same cells in two different companies packs with different "C" ratings on them. Some companies rate their packs based on a current draw that allows them to cycle many times, while others rate based on what you can get away with without destroying the pack on the spot. In the first case, the pack will last a long time, in the second, the pack will die after a much smaller number of cycles. Lipos do not take well to being discharged too quickly.

Oh, and finally, some companies have better reputations than others, and price isn't always an indicator. Several guys around here swear by some of the lower priced packs and swear at some of the higher priced brands.