Use the Hobie boat/parts catalog (and PDFs available online) to see exactly EVERY part you need for your boat. Even small parts can be very expensive. A very careful inventory of what comes with the boat is key to make sure you get your money's worth. Some interesting items - newer mainsheet system - $300-400. New tramp - $300-400. New gooseneck - $75. Shackles are $8. You can spend a lot of money on standing rigging alone, not to mention new main and jibsheets, downhaul, etc. Are the sheaves wrecked in any of the blocks (cheek block on mast is good example)? These blocks are riveted on and need serious work to be replaced. A missing gooseneck can mean removing rivets from the cap on your boom and replacement. Missing cleats on your mast mean work too (should be three on the old school 16 with normal downhaul, two riveted on and one in the track). Rudder blades OK? These are super pricey if not. A simple tiller extension is over $50 for the most basic one (if you want to replace it like I did, someone stuck a PVC pipe on my tiller as the extension). Come with trapeze rig? All bits included and in good shape? How many butt buckets come with the boat (you will probably want two of them and they are pricey too - old school if you can find them are $30-50, new type $100+). I found the hard way that my "free" Hobie 16 cost me about $700+ to bring back to life. New tramp, lots of missing small parts, missing gooseneck, busted parts on the mast, sails were not in great shape (bought a new set).
Amen on the standing rigging. It is not very expensive to replace the forestay, bridles, pigtail, and shrouds. You don't want a dismasting, and a visual inspection won't guarantee against a major failure of a shroud when under sail. Get the rubber coated stuff, and note the age of your cat. 70s and 80s cats have different standard length standing rigging. There was less mast rake as "standard" then. You may like more rake (this helps speed if you are serious about that).
Sails - Sun bleaching across the sail (usually near the bottom) means they probably wrapped the sail around the boom and left it in the sun. Bad news. The bleached spot will be weak and likely to tear. Mildew on a sail is a sign that the sails were put away wet. Oh, sails should be "crunchy" and crisp, not soft. If soft, they are badly worn and likely "blown out." Check to be sure the battens (the reinforcing sticks in the sails) are all there with the caps. If not this is a costly fix just for battens.
Look at the rudder cams (see the parts list for this). Are they beat to hell or in good shape? If beat up this may indicate the cam/plungers need adjustment, and you may need to replace badly worn cams. If the boat is really old like my 78, you may need to completely remove the old plunger/nylon screw and spring and replace the parts and tune the tension. Not expensive but a hassle. If cams look good you either have a much newer boat, or one where the rudder locking works fine so no one has been banging on the cams to get them to lock/unlock properly.
Also look for a righting system...at least a line tied to a pylon and coiled somewhere, but my favorite is the righting line sold by salt_city_sailing on Ebay. The guy makes them himself with climbing rated webbing and very strong shock cord. Super easy to install, and dead simple if you dump your boat. I have one on both of my 16s. Just grab the thing and pull when you dump over, no need to have pulleys, tie a righting line, etc. Just snaps back around the pylons when you don't need it.
Hope this helps.