Fiberglass, Carbon Fiber - Fibre Glast Developments Corp.
Jamestown Distributors
Fiberglass Supply (Surfboards, Windsurfers, Kayaks, Canoes, Boats , Autos and more)
These three had the best prices for fiberglass/cf when I did some fiberglass work for my friend. Looking at the c/f it gets a bit expensive. As posted above you might want to go fiberglass and overlay with c/f. This eliminates the need to vaccume bag and save some money. However it will not be as stong as all carbon fiber vaccume bagged.
edit: and it really depends what your constructing, you might have to make a mold which adds even more cost. All in all it might be cheaper to buy the c/f part if it's avaible (assuming the part is not a custom housing/enclosure ect.. )