[soulfuldog]

Further to what mr_nihilism has just posted -

Are you willing to learn how to remove DRM from ebooks and convert between formats?

If yes then you can take your pick of the market, but you'll struggle to find a new lighted reader for less than $100.

If no, then you need to decide where you are most likely to buy your ebooks from. If you are already a happy Amazon customer, consider the Kindle Paperwhite ($119), but you can't buy ebooks from other stores.

Or if you'd prefer not to shop at Amazon, you should look at the epub ereaders. The main two available are the Kobo Glo ($129), and the Nook Glowlight ($119), the Kobo is probably the better of the two. There are others available but I'm not sure how readily available the Bookeen Odyssey HD for example is in the US, and it's certainly not any cheaper.

Edited to add: You might be able to find the Nook Glowlight for cheaper right now, it's been heavily discounted in some places. If you have a Radioshack local to you, they've been on offer there.