Just to make things more difficult theres actually 3 different types of seales flat lock stiching (lets water in and stretches easily), glued and taped seams (doesnt let water in and doesnt stretch much) and also fluid welded seams (doesnt let any water in and stretches too) this is by far the best seam to get most durable and most comfortable.
A glued and taped seam should only be $50 more and is well worth it if you feel the cold at all. You can get oneill hammers or ripcurl$ classics sealed for $299 good value warm suits unsealed are 249 (price accurate last year).
If you want a good value suit I would recomend an o'neill heat they have fluid welded seams and heaps of stretchy neoprene. Theres also a quicksilver model with similar features, but cant remember what its called.Both these uits are about $400
If you wont the best suit money can buy then get the oneill psycho these are awesome suits and of the very best quality i ve got one

.
I would recomend going to a store that has a large variety of suits cos you need to try heaps on before you buy. Always go a bit smaller then you thimk cos they will stretch a bit in the water. Longreef surf has heaps and heaps of suits probably the biggest range in sydney and the best prices too.(used to work there!)