May be worth trying RAC online, then ring them and ask for a better deal.. especially if you do low'ish mileage and have a partner.
I got me (31) and mrs (28) insured with the RAC for £420 fully comp on our Impreza turbo (I know it's not a cossie lol but all other quotes were silly) It's 6k miles limited but she just pootles around occasionally in it (as we've just had a nipper) It was £480 online and I rang up and got a sound bloke, asked for a sunday special price and he got it down to £420 and threw in a years rac breakdown cover!
It might be worth a try. Her current insurance company wanted £700 TPFT on the same car for both of us.
The RAC insurance is the 1st cheap insurance I've experienced in my life and I'm sure they're a decent enough company (hopes)
Also, maybe some of you guys can get classic insurance on cossies now?