For a good condition LCII with a working display, keyboard and mouse, you'd probably expect to pay about US$30 tops. I'd probably look for one thats in the best condition as possible, and with as much RAM (they max out at 10MB, with two 4MB 30 pin SIMMs, and 2MB of the onboard memory - they actually have 4MB onboard, but if you max it out it will only see 10MB, even though there is 12MB available) and as big a hard drive as possible. (keep in mind they came with a 40 or 80MB HDD standard) Speaking of hard drives, stay away from the Quantum ProDrive ELS. Try and get one with either a Conner HDD, or better yet, a Quantum ProDrive LPS if you can. Also, the LCII, like all other LCs, has an LC PDS (Processor Direct Slot), which can be fitted with various types of cards - for example, you may want an Apple IIe card (which is basically like putting an Apple IIe into your Mac), or an ethernet card which allows you to connect to an ethernet network.
Also, another thing - does it specifically have to be an LCII? I know the LCII was your first Mac and all, but there are other, better, faster LCs out there, such as the LCIII, which used a completely redesigned logic board, with a 25 Mhz 68030 (up from the LCII's 16 Mhz 68030), and had a maximum of 36MB of RAM, and the LC475, which used a 25 Mhz 68LC040. These machines are better than the LCII in just about every single way, while sharing the same case and only taking up the same amount of space - the only things that the LCII has to offer that these machines don't, are a different boot chime (which you may prefer), and the ability to run System 6.08. (the LCIII and LC475 won't run anything below System 7.1 with an enabler)