Get a copy of Tape OP -- they usually preview several mic pre amps.
Also, your 4-tracker probably has mic pre amps, or a couple -- don't know which one you've got -- but, traditionally, mic pres on recording units are not the best but they are getting better.
You can also check out the Grace Design site -- but their mic pres are around 545 for the 101 model which I use; however, I also have an ART dual channel and it works quite well.
Keep looking and reading and try to get hands on demos before you drop your cash.