I know how you feel. I had my tank setup for a few months, with everything growing perfectly. I decided to pick up a... you guessed it, Kole Tang and it wrecked every fish but one. Dont give up. Do things right, no short cuts. If you cant afford something, wait till you can. Every time I take shortcuts, I get bitten.
After the wipeout, I reviewed my options and decided to do things the right way. I gave away the one surviving fish and went fallow for 72 days. The first fish after going fallow was a tang - which died right away. It didnt LOOK like it had ich so I had no idea what killed it. Frustrated, I waited another few weeks before getting another shipment from a reliable source. This time, everything worked as expected and my tank is better than ever - ich free!
I will not trust anything from this point forward. I'm going to get another tang eventually but only after it's been QT'd.