Do a search on Ebay for a QRP transceiver, you'll probably see a wide range. In the $400 range you probably could get an early model Yaesu FT-817 . I have a FT-817 for portable operations, it's a versatile radio that covers HF, VHF and UHF. If I remember, after the holidays I'll put up some photos of my portable set-ups.
Another Yaesu radio which I've had experience with is the FT-7, which is 10 watt HF rig. I've seen them on ebay in the $200 range. They are a simple radio, easy to use, but efficient.
MFJ makes a multitude of QRP radios, and I've had good luck with them. I have a 9475 and a 9440. Again they're simple one band radios, I like them because the radio, a small power supply and a wire antenna will all fit in a typical ammo can. They're basic enough, that you could give them to someone with limited radio experience, and they could get on the air. The 94XX series are perfect for camping. However, they do cost a little more than your budget, and they're limited to just one band.
There's a multitude of kits available, mostly geared towards CW operations, but there's a few that do operate on SSB and the digital modes. Among these types of kits are the Heathkit HW-7, HW-8, and HW-9 CW transceivers. The HW-7 is the ost basic, and you should be able to find one in the $100 range, and HW-8's in the $150 range. I have a HW-7 or 8, I'd have to check, it resides in another one of my camping ammo boxes. I do loan that out, along with the MFJ QRP radios, to newly licensed hams, so they can get some HF experience.
I've built a few CW kits including the Lectrokit Spider CW kit. Most of the kits do require basic soldering skills. I would hesitate to purchase a kit used, because you don't know how well it was assembled, and this applies to the Heathkit QRP radios too. I've been looking at this QRP SSB 75 meter kit:
http://www.qrpkits.com/survivor.html Maybe Santa will surprise me!
