Well if you get a combined preamp/soundcard for less than $500 then your preamp will be your weakest link.
You can get an Echo Mia on sale for $99 at GC from what I've read. That leaves you $400 for a preamp. You could nearly afford an RNP which would be a class above any preamp built into a soundcard (or budget mixer) or get a dmp3 and still have cash leftover.
An M-Audio delta 66 omni studio is less than $500. I'm not sure if that qualifies as a combined soundcard and preamp or is considered a separate preamp/mixer and soundcard?
More important is how many, and type, of analog and digital i/o you need, and how many mic pres you need.