Hi, you have 3 options. you can either get an aux in cable from fiat (or ebay etc), a different head unit or you can get an FM transmittor. The last one is the cheapest (between £12-£30) but is also the lowest quality. I went for one and it's ok, but not great.
I asked the dealer (evan's halshaw) about an aux in cable, and they quoted me £150 fitting. Should be ALOT cheaper on the web if you can fit it yourself so good hunting!
A new head unit will set you back about £80-100 ish for a decent one with aux in on the front (3.5mm jack) + USB port. Some of the more expensive one's will also control your IPOD throught the head unit. You'll need to fit a bracket and it won't look as good as the original FIAT one in my opinion.
There are a couple of threads (i think) about head units and the aux in option, so you might be able to find a better answer around here somewhere.
Whatever you decide, good luck
