Author did a nice job writing up converting a 4 foot Fluorescent fixture to LED for $30. I think it can be done for $20 myself and that includes powersupply. Funny thing is this is only a little more work than if you did the conversion with LED bulbs (since you have to replace the ballast anyways). Oh and that route will run you at least $40, thought they would look nicer. Another bit I would change, I think I would use something in addition to the sticky tape to hold the LED strips in.
http://www.instructables.com/id/Fluorescent-to-LED-conversion-under-30/