Order the Hobie catalog here on this website. It comes quickly, and with a full price list. I have found that most of the parts on ebay are not that much a savings from new for the parts that are commonly needed.
Also, never buy used parts for the parts that wear, as they typically have little life left. Used shrowds, used rudder cams, etc, are really never a smart buy for safety reasons. You want new there.
Elkyjason, not challenging your experience, but I have read quite a few positive comments about the ebay trampolines on this forum. It won't be class legal, but if the boat is more than 10 years old you probably won't be racing in a hobie sanctioned event anyway, and they will probably give you an exemption if you are a noob on a very old boat.
I did the same thing you are doing about 3 years ago, although I had most everything I needed in mostly working order when I got the boat. I am in a freshwater area, and haven't heeded my own advice to replace the shrowds, although I don't have coated wires, and I inspect them often. I did replace many of the lines and sheets (ropes) with Home Depot rope, and it worked to get me on the water. This summer it is clear that they all need to be replaced again, and I am getting the good stuff from my local Hobie dealer. I replaced the rudder cams, and on this boat it made a world of difference. I completely disassembled and cleaned the rudder system, and shimmed it all up to make it work really nicely. I just bought new sails, but probably didn't really need to, but I really liked the colors. I am just about to replace the tramp, and will probably get one from ebay.
My advice would be to do what you can to quickly and inexpensively get it on the water, and start enjoying it (within safety limits). Either read EVERYTHING you can on here about sailing, and RIGHTING your boat, or hook up with some other sailors locally for the first few times out, even take one out with you if you are just learning everything. Quickly you will be hooked, and gain knowledge and confidence. Over time, you will learn where the money is best spent on improvements.
Welcome to the forum! Go sailing!
1979 Hobie 16 "Orange Crusher"