You can setup paypal with a debit card, it will just go thru as credit. (unless your card doesnt allow credit type transactions, not sure if theres any that dont tho.)
another thing that you can do is buy a prepaid creditcard. I used one of these for online just to keep everything seperate from my bank account.
Just go to the bank, buy one in 25/50/100 amounts, and setup a paypal account. when its out of money, its out of money. buy a new card or go without the app.