I need advice on a 5 speed

So thanks to the amazing tax returns this summer i will be putting a T-5 in to my 89 GT which i blew the AOD up last summer. I'm looking for something a little step up from stock but not fully blown crazy! something in the price range of $500-600 that could handle maybe 300-350 HP. I Live in Illinois and I am willing to go pick it up somewhere near the greater chicago area but shipping is ok too. But i want this to be completely rebuilt and new! and another thing is that there can't be a hefty core charge b/c i only have the AOD to give back which is usually not substitutable. anyone have any ideas on where to get something like that? someone i know suggested astroperformance.com but their core is too heafty for me.

Thanks!!