Yes, it would be appropriate to have a Marine surveyor conduct a survey. It is not the $5K you may be willing to gamble but these days it can cost a couple of Thousand Dollars to dispose of a boat which is found not sea worthy. Furthermore when you go to insure the boat the Insurance Company is likely to require a survey; might as well get it up front. Many times items found during a survey can help a buyer get a reduction in price.
I think that is generally good advice but I will offer up a counter point view. You are looking at a 30 year old boat that was on the low end when it was new. You are not going to insure it for its value. Just get liability and that should be in the few hundreds of dollars a year range. Mine is insured through State Farm and bundled with my homeowners. So, I'm not recommending you hire a surveyor. You just are not investing that much money. Find an avid sailor near where you live (this forum is a good place to search) and ask if they will go look the boat over with you. Also, you have to get mentally strong and not look at the cosmetic items...(but that can be hard to do) a 30 year old boat that has sat on its trailer can be ugly but otherwise sound. Just remember a pressure wash, buff and wax can do marvelous things to a boat.
I have bought, fixed up and flipped seven old sailboats over the years.
... here are the things on my list when I look over a boat.
1) What does the trailer look like? A new trailer and trailer repairs will cost you real money. ($2K) Look hard at the trailer.
2) What condition is the outboard? A new O.B. and O.B. repairs will cost you real money.($2K) Does it start by the third pull? Was it already warm when you got there? If so, the owner may know it is weak and he primed it before you got there.
3) What condition are the sails? (You may need a sailor to go with you on this one) New sails will cost real money ($2K) and old blown out sails will make you hate the boat. You are no looking to see if the sails are clean. You are looking at the shape and if the fabric has stretched.
4) What condition is the standing rigging (the cables, a.k.a. stays). The the chainplates (attachement points) solid? Rusty? Do any of the stays have broken wires? Rub a piece of cotton on the stays and if they snag cotton then they are shot. If they are shot you can expect to pay up to $1K if you do the work yourself or more if you hire a rigger.
5) Is the mast straight and solid? If not walk away from this one.
Next start looking for any signs the boat hit the bottom hard. Are there chips missing from the dagger board? Are there any cracks around the board's trunk? The macs do not have a cored hull so no worries about soft spots... and cosmetic fiberglass damage above the water line are relatively easy fixes that people here on this forum can walk you through so don't let those become an automatic "no". Also gel coat spider cracks are common and only cosmetic.
If 1 through 5 are all good, the boat is worth $5K. If the boat is cosmetically clean, updates to equipment have been made, the O.B. and sails are less than three years old, the trailer is freshly painted and has newer tires.. you may start getting close to $10K. If anything in 1 - 5 is questionable, you should think real hard about how bad you want this boat. Are you handy with carpentry and paint? Can you weld (trailer)? Are you mechanically inclined (O.B.)? etc. Also, do you have a shop to work on the boat? How much do you enjoy tinkering or would you rather be sailing right away?
Expect to have to replace all of the running rigging (ropes). Expect any wood will need a sanding and a fresh coat of varnish. Expect the hull to need buffing and waxing. Expect to replace the carpet inside (carpet tiles are the way to go here). Expect the cushions to be musty and need cleaning and maybe a new covering. Plan on replaceing all of the light bulbs with LED bulbs. These things can be done a little at a time while you enjoy the boat.