There are indeed a couple of working testnet faucets. (I used to google for them.) But the amounts they give are usually small. You'll need a huge effort to gather big amounts like the 50 tBTC OP was asking.
I find mocacinno's offer reasonable. Basically OP would only lose the tx fees for the collateral, since he will return the loaned tBTC (and if any tBTC is lost for fees, that can be recovered from faucets).