For used there are much better things to be had for $300 to $500.
I started with a Cambridge C500 preamp a few years ago when I first wanted to play around with separates. I say a few year ago, because I was probably the first person in the country to have one. I got it from a dealer who had dropped Cambridge, but got one by mistake from the distributor as a pre-demo before they were to start selling them. So he sold it to me for about dealer cost. It had the optional $60 phono stage. I only paid like $225 for both. My first power amp was a Conrad Johnson Sonograph set that I picked up used. It had the SC26 preamp with the SA250 Power amp. So I got to do my first showdown in my home and the Cambridge was slightly better than Sonograph preamp to my ears. Since the Sonograph was a $1000 new list price preamp, I was impressed. I kept the SC26 in the closet until I resold the SA250 later.
The C500 is very neutral for an inexpensive preamp. It does not add or subtract anything from the sound that I could hear.
My next step was an original Conrad Johnson tube PV-10 pre I picked up used for $525. (Another one with phono; a must for me). It was a very noticeable improvement, which is why I said if you don't mind used, you can go much further for $500. The SA250 amp was replaced later by the CJ MF2100.
I now have a solid state CJ Motif MC-8 (great phono) with a Blue Circle BC-22 power amp. It really sings!!
You may want to stay away from tubes starting out?? For solid state used under $500 you may find older Conrad Johnson's PF-1L, PF-2L, Superphon Revelation, Acurus RP-11, various Bryston and Adcom.
For a new C500 there is a demo at AudioAdvisor.com for $229 and the phono for $50 if you want that. They have a 30 day return policy which gives you a change to try it.