It seems like the first question would be 'what condition are the sails in?"
That will be $1500 new or $300-800 used to replace.
What I would be looking at would be, in this order:
Start at Zer0 value -
Good solid hulls, worth $300
Good usable sails - $400 for recreational sailing, up to about $800 for prestine
rudders complete in good condition - $200
Solid usable trailer - $400
Trampoline that doesn't need to be replaced - $100
Complete with all the other hardware - $100
This will give you a good idea of where to start. The key on a 30 year old boat is that it will be used for weekend, recreational use I assume, so making sure it is serviceable and usable is key. Plan to have to replace some of the rigging if it is a freshwater boat, all of the rigging if it was a saltwater boat. All the lines will need to be replaced, but you can do much of that with $20 worth of Home Depot rope. This will get you started and on the water. Trust me, if you fall in love with it, you will want to start upgrading things and you can do it over time as money is available. The key to start out is to get a boat at a reasonable price that you can just hop on and sail. Once you get it, post some pictures and ask questions, the guys on here have seen it all and will tell you how to do anything. My only caution, and I REALLY don't mean this as a slight, is that most of the guys on here are pretty serious about their sailing, and meticulas about their boats. Some of the advice on here is geared toward the competitive racer, not the weekend guy who just wants to get out on a boat for a couple hours before the BBQ starts, so while there way is definately the RIGHT way to do it, there are many times much cheaper ways to do things to get you started.
I rigged my boat with Home Depot rope. It works fine for me while I am out learning on my cheap old boat. Someday, as I get better, I plan to upgrade all my running lines and sheets, blocks, etc. But for now my ropes abilities far excede my own!
Have fun, keep asking questions, buy a damn boat already!!
1979 Hobie 16 "Orange Crusher"