RockHill, welcome to the forum. We all have to pay the price for wisdom and I would say you got a pretty good dose! I think we can salvage most of your investment here and hopefully get you out on the water. I think your boat is repairable -- here's how I would proceed at this point:
1. Examine the boat thoroughly and look for any other signs of damage, concentrating below the waterline. Pay particular attention to the drivewells, looking for any cracks in the plastic. If you find nothing else suspicious then you can proceed. BTW, you can determine the year model by looking at the serial # on the bottom near the stern -- the last two digits will be the model year. It's good to know this if you need parts later.
2. Lets get started with the repair. Ideally you can procure some matching polyethylene (PE) to cut up and use. Hobie would be your best source for a color match. Dealers don't necessarily carry scrap plastic but one might be willing to ask Hobie to send some. They are not under any obligation to do this for you so be nice if you want their help! Otherwise, we'll move forward anyway.
You're going to need some special epoxy -- either 3M Scotchweld DP 8010 or Loctite 3030. These are the only two epoxies that I know of that will form a strong bond with PE. You don't need to rush out and buy any special dispensers -- read here for links more specifically related on tips working with these products, where to find them, etc:viewtopic.php?f=11&t=48538&p=216118&hilit=scotchweld#p216118
3. Lets remove the mast receiver. It screws in from the top so open the nearest hatch, grab the tube and unscrew it. Withdraw it from the top and set it aside.
4. Next lets patch the hull from the inside. Cut out a patch from any material you can find to fit over the hole. Heat it enough to shape it to match the curvature of the hull as close as possible. You'll mix about 1/2 of a small epoxy kit to bond and seal around the hole perimeter. You don't get much working time with this stuff so have your job laid out and rehearse the set up. Be sure to use latex gloves. Let it set up for a day. This should restore the watertight integrity of your hull.
5. The next job is to reinsert the mast receiver or mast step. You need to find or build either an inside or outside mount that will permanently sit inside the bottom and anchor the mast receiver. This sits inside and permanently mounts to the bottom of your hull. I'm thinking about an inside mount PVC end cap that slips in the bottom of the tube -- fatten it up with glue or slim it down with sandpaper as necessary for a reasonably snug fit. Clean up the bottom of the tube. If you bring the tube with you to Home Depot or Lowes, etc, and snoop around the plumbing isle until you find something.
6. Using a stainless screw, anchor the bottom of your end cap to center of your former hole to align it with the mast step. You're going to screw this in from outside the hull. A dab of glue/epoxy will keep your base from unscrewing over time. Trim the mast step to the new correct height and screw it in place. The screw head will be sealed and buried under your outer patch, which we can address next.
7. The outer patch is for extra strength, and can be as cosmetically nice as you want to make it. If you're not an experienced plastic welder and can't get suitably matching PE, you might just as well return the welder. You can glue and patch this, pre-shaping your patch as much as possible, filling in with epoxy as necessary and sanding everything flush when set-up. If not pretty, it will be streamlined, solid and ready for the water!
The forum is here to help you. Ask if you have questions. If you take some pics along the way, you might be able to help someone else with their problem. Good luck!
PS. Hobie dealers are independent businesses. They do not work for Hobie and are under no obligation to service anything they did not sell. They can choose not to do business with certain customers that piss them off. That said, most are more than willing to help out and would probably like to earn your business. Hobie reps work for Hobie and are there primarily to assist dealers. Anything you need from Hobie is done through the dealer network. Going forward, you might keep that in mind for best results.