I'm in agreement with the responses above.
If you're set on having a separate preamp in front of your recorder, the MixPre/FP24 is pretty hard to beat. Virtually bombproof and transparent, they can easily be had in your price range on the used market. No personal experience with the Audioroot devices but they do have good reputations.
On the other hand, acidjack's suggestion of an all-in-one is very solid. The newer recorders tend to have very good preamps and it's one less box to cart around. In addition to the Roland R-26, I would also recommend the Tascam DR-60D. While it's form factor is a little different (imagine a brick of butter) it seems to have far fewer complaints than its newer sibling, the DR-70D, when it comes to handling SD cards.
The one caveat that applies to all of these devices is that none of them have digi in/out. Don't know if that's a requirement for you but something to consider if it is.