I did the exact same thing, bought like 20 of the (2 5/8) spring clamps, and about a dozen-odd 3 and 6 inch c-clamps.

They've been working fine for gluing the frames, and skeg.
haven't gotten to the gunwales yet (which is where i see my current plan may fall a little short).   

Co-worker notified me that he ordered a BOX of spring clamps through amazon (4" or 5"), and they ammortized out to about $0.65 a piece (not sure how many... 30? 50?).
Cheaper than the BOX-Stores by far though.
They may have a similar option for 3" C-clamps too. (prime = no shipping cost).

Check it out.

ASSuming you're not doing scuppered inwales on your ENP, 2-5/8" is  wide enough for the rub rail, which is really the only place/time you need an obscene amount of clamps #neverenoughclamps...