Used T5 fixtures are usually pretty easy to find, like this one:
http://www.canreef.com/vbulletin/sho...threadid=98752
Running four bulbs would make a huge difference over one and allow you to use a mix of spectrum including blue/actinic which is what you need.
For cheap LEDs the cheapest option is probably the D120
http://www.reefsupplycanada.com/d120...ight-16-light/
I assume one will cover your tank. Anything cheaper will likely not produce good results.
10% water changes won't be effective for nitrate reduction, better to do as close to 100% as you can.