I’ve just purchased the HiTech filter system (1,2, and 3 stop ND soft grads and a 10 stop) and it’s pretty good. Couldn’t tell you about Cokin but I would recommend HiTech no problem. No long delay either.
The Hi-tech are ok, unless you want to stack them, in which case there is a noticeable colour cast. They are also thinner than the Lee’s, which isn’t a good thing.
Wait for the Lee filters. If you buy cheap, you buy twice.
You could also try Tiffen filters. They are big heavy chunks of glass, used in the motion picture industry for years. They are not cheap, but by many cinematographers they are seen as the best. The build quality of Cokin compared to them is nonexistent. You can get them in a whole host of different sizes and also as screw in. I compared them to Lee myself. I’ve heard that stacking Cokin filters will cause a colour cast, but have only heard good things about Lee.