Ah, Man O War, GWs second best game ever
I can't help you buy ships, but here's some links if you want to think about making your own. Even when the game first came out, I thought the ships were priced way too high from GW. Since I was making fleets in bulk, I just did very simple modelling, they went up quite quickly and easily. I got fancy on the sails, which was fun. You can make the models as simple or as fancy as you like.
There's a Yahoo discussion group:
http://games.groups.yahoo.com/group/theseaofclaws/
And they have an overflow site for holding files:
http://groups.yahoo.com/group/manowargame
If you go there, I have pictures up in the Photos section "Maureen's Fleets"
And a description in the Files section "Notes on Maureen's Fleets"
Hope that helps!
Cheers,
Maureen