I was in the game for several years. I was very honest and very fair and did not up sell or otherwise fix things that the client wasn't paying me to fix. Being in that game, I would often see machines that my competition had previously worked on. I knew the quality of the work they did and I knew what they charged for it.
Saw a lot of shoddy work. Saw a lot of shops that would just start throwing parts at the problem (on the clients dime) instead of doing any actual troubleshooting or testing. Oh we think you need a hard drive so we'll replace that (and just clone the existing drive and its problems). Whatt'd ya know that didn't fix it, must be a bad memory chip. Nope, that means its gotta be the power supply but tell ya what, since we already chanced this other stuff, we'll give you 10% off this power supply that we already marked up 100%. Saw that a lot. Then I'd be called in, spend about 10 minutes diagnosing, back it and whack it (which should have been done to begin with) and call it a day.
Like I said, I saw that kind of thing a lot. So... I say again. If you have a shop that you can trust, as in you have a history with them or someone you know well has a history with them, then take it there and let them fix it. Absolutely 100%. But if you don't know of anyone trustworthy to take it to, well you can roll the dice if you want but you should know that rolling the dice is exactly what you'll be doing.
But keep in mind its a 5-year old machine. Most shops won't even take a peek at it for less than $100. Spending $250 to get it back out the door isn't hard. Nor is spending more. So now you're a couple hundred in and what do you have? A 5-year old machine. Are you going to get another 5 years out of it?
Or the OP can do the work himself if he wants to spend a few years learning the basics and probably letting the smoke out of a few parts along the way.
As for your airplane/avionics example? Airplanes and the avionics that go into them are not generally considered to be disposable items. Computers, especially windows computers, for the most part are. Its not quite the same as taking a pic lighter in for repair but its not far off from that. If you can do the work yourself or you know someone that will do the work for you for free, they're definitely work fixing. If you need to take to a shop, let them diagnose and get a quote in writing before they do any other work. I just do not see the wisdom in spending more than $200 on a machine that old. You're free to disagree and obviously you do. The line of people that disagree with me forms over there. Its a long line, bring a lunch.