Jurassic park is a great first pin to get, but I would recommend getting one from someplace other than an estate sale, preferably another pinball person if you can. Do not purchase that machine if it is not plugged in and fully functional when you go in to see it, unless it is super cheap. I would recommend that if you see the machine and it's turned on and fully functional, you offer no more than $3,000 for that machine. If it is folded up in a corner in the garage and hasn't been turned on in years, offer $2,000 for that machine. Plan on the estate sale wanting too much money for that machine, and getting the price range off of Ebay. What you want to do is contact the estate sale and offer those prices as given above, and tell them if they don't get the outrageous price they ask that you would be willing to take it off their hands for 2k or 3k depending.
If you have a chance to look at it in person and it cannot be turned on, walk away. If you have a chance to turn it on and it doesn't work, or you open the back box and you see leaking batteries onto the circuit boards, or evidence of it in the past, run.
If it turns on but the TREX doesn't move side to side and up and down, subtract $500 from the offer and plan on 8-10 hours of troubleshooting and parts.
If it turns on but looks like all the rubbers are rotting off, this is a good sign and an easy fix.
I would recommend getting a fully working pin for your first... especially something you can test and play. Replacing bulbs and rubbers is mechanically simple, and you'll do fine. You will do much better if you have a pinsider or someone who has owned the game for a while and operated it explain to you how to do the basics.
Jurassic Park is a great game and probably my favorite of those I've owned (Attack From Mars, Stern Star Trek, World Cup Soccer, Pinbot). It is a great game in a one game lineup and fun to play, modify, and looks cool in the house. I would absolutely recommend getting one, but would make sure it worked if it was your first pin.
I've had mine 3 months and in that time I have had to do some minor soldering to fix the TREX, some troubleshooting to fix the ball trough, replaced all the lights with LEDs (easy) installed a few mods (easy) and replaced the rubbers (easy).
Long story short, get a Jurassic Park, but make sure it's one that is fully working if it is your first pin. It will break slowly over time, but starting from a working game is much easier than starting from scratch.