If you're commuting, go rigid. There are several on the market. Surly's would be fine, or Kona's Project 2. Of course DeKerf's own tuning fork would be ideal, but I think you'll find they're a bit more than $300. Hell, if you could find one for that you'd be a fool not to grab it.

If you want to keep a suspension fork, perhaps you can just rebuild your Judys. The process is straightforward enough, but parts might be an issue.