The sun/UV beats up paint and gelcoat all the same. Gel coat is easier to restore than paint, which will either need to be re-painted over, or stripped down and then repainted. With a regular coat of wax, gelcoat will remain glossy. Gel coat is much thicker and provides more protection to your hulls than paint. If gelcoat starts to fade, it's a simple process to buff it back into good shape. Gelcoat is made of polyester resin, the same material the rest of the boat is made of, so it will adhere perfectly. It's purpose is to protect the fiberglass from oxidation, UV damage and water absorbtion of the fiberglass. Paint is somewhat less effective in these regards, and will start to fade, crack or peel later down the road. There's a reason that nearly every fiberglass boat on the water is "painted" with gelcoat! Unlike paint, brand doesn't really matter, it's all the same product. Spraying gel coat, if necessary, can be done in the same way as paint, with a typical air compressor, cheap spray gun and some thinner. It's a very involved project though, so better leave that until the winter.
This article is an excellent how-to that will tell you everything you need to know about gelcoat restoration: http://www.fiberglassics.com/RESTORATIO ... G-GEL-COAT
All that said, I would have serious concerns about the structural condition of a boat selling for $300. Maybe the owner just wanted to get rid of it, but more likely it's seen years of neglect long before he decided to sell it. I would check every aspect of that boat for soft spots, loose rivets, cracks and frays, etc. Note that most everything on a Hobie is reparable, aside from widespread softness of the hulls.
Take a good look at the rigging, too. Old rigging should really be replaced, especially if it shows any signs of wear, stress, fatigue or fraying. Shroud anchor pins too, as these can fail almost without warning when fatigued. Check the forward crossbar for any cracks. If the boat is stiff, the hulls are solid and the rigging is good, you've got a good boat! If any of these are compromised, they should be repaired or replaced. Otherwise it could lead to a dismasting on the water, which can be very dangerous.