Is it normal for pricing to jump 20-30% in either direction in a few days?
The prepaid rates are rarely worth it ( 10% rebate or so) as the rate swings are normally higher. Check .com .de .co.uk ..... As they will all be different ( on one site a Audi TT might be expensive on another just a little more than a Golf). Paid at pickup and check/rebook regulatly