pinwiki.com has a good repository of information.
Could be dead/missing batteries, or the batteries may have leaked on the MPU. So, at least, you'll have to deal with batteries, at most, MPU repairs or a replacement.
Plus all of the issues that go along with a game that hasn't been serviced in a while--mechanical issues, lamp issues, coil issues, possible reset issues.
A project game is cheaper, yes, but there can sometimes be a few hundred dollars in parts that go into it. For a decent shop job, I usually spend around $300-$600 per game. But--it's that somewhat on the low side since I can normally handle pretty much any repairs on my own and don't have to send out boards for repair.
Quoted from Rewdood:I am mostly just wondering what a fair price is on a machine that might need major repair
It depends on the condition of the artwork and playfield, and what repairs actually need to be done.
With fish tales, the cabinet is usually faded, there is typically wear around the playfield inserts, and the topper is sometimes missing. All of that decreases the value.
Depending on what state it's in and the condition, maybe anywhere between $1000-$2500.
But, if you're up for it, decals and replacement playfields are available if you want to do a high-end restoration. That's a lot more expensive and time consuming than just a shop job, and I don't recommend that for a beginner since most people just want to get a game up and running and start playing, and beginners can sometimes lose interest in a project that will take a few months to work on.
It depends on how interested you are on seeing a project through. A lot of us got into the hobby by fixing or acquiring a broken game.
Some people just like to play, others like to repair, do research, document, collect, bargain hunt, compete in tournaments, go to shows....there are several aspects to the hobby.
If you think repairing games is in your lane, there's a lot you can explore in this area.