web app almost finished, how much for a design?

I've been working on my app for a few months and feature wise, it's ready for a beta. However, due to a) my general hatred for working with css b) my complete lack of css and creative skills, all the output is bare, unstyled html

I have $300 to spend. Is that a realistic budget for hiring someone to skin the app? it's a very data heavy with lots of data tables and graphs, so I'm not looking for a "site design" or branding. I'm looking more for a simple and clean user interface. I'd be happy with a set of styles for standard elements such as forms and tables.

is $300 unrealistic? if so, would people recommend launching (private beta) as-is or wait until I can afford a designer?