You should calculate your prepaid amount* in this way:
Prepaid amount* = $10 (weekly rental) * X (weeks) + $10 (shipping fee) + $100 (deposit)
For example: if you would rent it for 1 week, the prepaid amount is $120* = $10 * 1 + $10 + $10
if you would rent it for 2 weeks, the prepaid amount is $130* = $10 * 2 + $10 + $100