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.
I make the assumption that anyone asking for large amounts of testnet coins is a scammer looking to rip someone off who does not understand the diffidence between mainnet and testnet. It's also a somewhat trivial programming change to mask the fact that the reference client is running on testenet. Probably other clients also can be changed somewhat easily not to show that it's on testnet.
But yeah for programming 10=1=.1=.01 should not matter how many coins you have.
And if you are any kind of non scammer you can just rent hashrate be it at nicehash / mining rig rentals / wherever and for a few bucks get them yourself.
If you have a real project it's just the cost of startup.
-Dave