I'm currently on vacation for the rest of this week. On Monday I'll try to come up with a reasonable collateral estimation to cover 50 tbtc.
Sooo... I'm taking a raw stab at this... To be perfectly honest from the start:
THIS IS NOT A SALE...
If this is not a sale, you should not be involving money in any way in any transaction involving tBTC.
It would probably also be a good idea to tell the people who are posting nonsense that they need xx tBTC instead of 0.00xx tBTC that faucets give out, that there is no reason to need a specific amount of tBTC. Frankly, if you are unable to adjust the code in your application you are testing to account for the difference between 50 tBTC and 0.0005 tBTC, then your application is not ready.