First, I strongly encourage you to keep VC-17 or SR-21 on the boat. In my experience, it is the only type of paint that works well on Lake Michigan slime. And if you cover over it with something else, you will need to take that new paint off if you or the next owner ever wants to go back.
If you are looking to save a few dollars, West Marine private-labels SR-21 as WR-21 and you can usually find it on sale in the spring for under $50. You can apply SR/WR-21 on top of VC-17. Both West and Pettit representatives have told me that the only difference between the Pettit and West versions is the label on the can (and the price).
Either VC-17 or SR-21 are very thin paints so a little goes a long way. We are able to get a coat on with three quarts, including