Some good advice there Vix, like it.
If you like the MK1 shape and a convertible then look for a sportline or a rivage (I've got a rivage so slightly biased). The sportline is a car that can look good modded, but I think the rivage looks better as standard, but that's just my opinion, plus the benefit of getting a newer mk1 cab is that they did make them until 93 so it's going to be younger than a hard top which stopped production in 83ish (I think).
I personally don't think that cabs are more trouble than they are worth, I love mine and with summer round the corner, enough said. Just make sure that the hood is in good condition otherwise you'll need your swimming trunks on to drive it ! Have a look at autotrader's website, there's usually a couple of Rivage's and a few sportlines on there. Don't know about the sportline, but they only did Rivages from 91 (J) to 93 (K, possibly a few Ls too) and they only did them in Blue and Green, oh yeah, and make sure they have the Rivage alloys on them too. Hope you find what you are looking for and if you need to ask anymore questions about running a cab then give us a shout.