Second most subjective topic in audio.
I'm considering the preferences you mentioned, foremost the Hafler 101. From that, the first preamp I'd look for, would be an APT Holman. You can pick one up cheap if you are lucky. I just looked at eBay and a few sold for between $107 and $350. If you have a few extra bucks, take a look at the Marantz Model 7T and if the Marantz appeals to you - but its over-budget, you might look around for one of the later, Sun Valley Marantz pre-amps or even one of the integrated amps with pre-main plugs and just think of the extra power amp as a bonus. Yes, it's totally subjective but the Hafler 101 has been part of my journey.