For simplicity sake please send $600 because it will be better to return to you as a round figure. You will receive 6x $100 weekly repayments.
I don't want to ruin your deal, it’s great to see an initiative like this as well as a @condoras desire to help.
you may not have best defined this deal. Jolly you will probably repay value in USD because you tied it to some secure income. But six weeks for the value of bitcoin is a very long period, and it can very easily happen that you end up paying less bitcoin, and yet you sent in all $600. which would be unfair to the lender, who gave a loan without interest.
Just my 2 cents here.
btw. good luck with this action, you have my support. Unfortunately, I can't help right now because I also struggle with doctors, surgeries.