Free rental is possible in the moment when your level-up, but rental time is only two hours (with a trick available to stretch it).
Paid rental (24 h) is available for 15% of the price anytime after you reached the level.
In both cases, buying within 24 hours will give you a 10% discount. Unfortunately, the full price tag's amount must be available in your purse though only 90 % are deducted.