I just ordered:
a small battery powered fan to put next to my bed.
Some battery powered LED sting lights for inside the tent.
A hanging closet organizer to hang in the tent to keep all my small bins and whatnot organized and easily accessible.

One of the best portable phone chargers I have ever used (though its $5 over your limit): http://www.amazon.com/gp/product/B009V5X1CE/ref=oh_details_o04_s00_i00?ie=UTF8&psc=1

Someone else suggested this same fan (but here is a link for $9.99 instead of $19.95) I used it last year in my tent and it worked great: http://www.amazon.com/gp/product/B001AVMSEY/ref=oh_details_o00_s01_i00?ie=UTF8&psc=1 (thinking about making a swamp cooler with this fan and a styrofoam cooler this year!)

If your car camping, this is can charge/run 7 different items at once: http://www.amazon.com/gp/product/B00EY6RJKA/ref=oh_details_o01_s00_i01?ie=UTF8&psc=1

Also if car camping, and will need to run your car at all to charge things, a flexible duct to route exhaust out of your campground is invaluable!: http://www.amazon.com/Dundas-Jafine-BTD48TC-ProFlex-Transition/dp/B0015UGPWQ/ref=sr_1_3?ie=UTF8&qid=1396231801&sr=8-3&keywords=dryer+vent