Why a mic pre in that range? ?
I promise I'm not trying to be an ass, but I've done a ton of recording and even worked in studios before, and IMO hardware mic pres aren't remotely worth it at that price point. Especially for recording guitar.
Once you get into the Uber-expensive zone, yeah, definitely they can be worth it.
But the lowest price point of a mic pre that would even be an improvement over the average project studio interface (or analog mixer) would be like the 500 series API 512 or warm audio WA73, and those are around the 700-800$ range IIRC.
It just seems like you've convinced yourself that a super budget mic pre is gonna make this huge difference in your recordings, and I can promise you, it's not. ?
Edit: a nice ribbon microphone or another auxiliary mic that you don't already have - a 421? Sm7? Seems like it would be a vastly superior expenditure of funds, as far as dollars to usefulness goes