Also suggest you look at this thread on the Happy Campers website for lots of discussion on bell tents: www.thehappycampers.co.uk/forum/viewtopic.php?t=166.
We bought a bell tent from Holland www.obelink.nl last February and haven't looked back since. Most of our camping last year was done in more or less torrential downpours and, even though our tent has no SIG, we never had any leakage problems even though the ground was often sodden. We had a bit of condensation the first time we used it but I think the soaking it got effectively proofed it and we didn't suffer again.
The only problem with a canvas tent is the need to dry it thoroughly before storing it which does mean you either need a spell of dry weather or have to be prepared to have it draped over your stairs/living room floor furniture for a few days unless you have somewhere else you can dry it, but to be honest I think the hassle of that is worth it.
Bell tents are really quick to put up and being able to roll up the sides on a hot day definitely makes them pleasant to be in - you can lie in much longer than in a nylon tent. This is one good reason for not getting a SIG. Another is not having to fold up your tent with a muddy groundsheet attached.
You will be the talk of the campsite too - everyone comes over for a look.
In my opinion, they're worth every penny but I would shop around. Ours from Obelink was 159 euros plus shipping (15 euro I think or thereabouts) - they have gone up to 195 euros now I think but that is still a fair bit cheaper than lots you can get over here. You do have to order in Dutch though which is a bit of a challenge. Lots on the link above about that. Otherwise, Soulpad www.soulpad.co.uk ones look pretty good.
Whichever you choose you will love it I'm sure