#1
 Tl;dr: Refret guitar at the cheapest store for 200 or at a real repair shop for 550? Also, why the huge price difference?

So I plan on refretting my rather newly acquired guitar as the frets are really worn down. I contacted the "bigger" music stores in my area and asked for the price, however, they range from 200 up to 900 USD.
As most musicians out there that are students and cannot work, I am a cheap ass and want to take the guitar to the place where they charge 200 USD. It is a music store that has four stores at different places (called "Blue Wonder"). Never heard anything bad about them and whenever I buy something from them they give good advice.
There is another store, which specializes in repairing guitars and is kinda known worldwide ("Guitar-Repairs Urs Winkler"), charges about 550 and is also the store in which I have confidence, as I know the owner very well.
The last store is basically the biggest music store here in Switzerland ("Musik Hug") and has great reputation. Refretting costs 900 dollars, so I can't even think about doing it there.

Intuitively I would go to the guitar repairs store to let them refret my guitar but there's the price, being twice as high as the cheapest one.
Questions: Why is there such a huge price gap and does it even matter where I refret my guitar, as long as the store is a decent one?

You may keep orthographic mistakes as English is not my native language. 
#2
200 is probably "I know how to do it but I'm not going to do a great job"
900 is probably "I have no idea how to do it so I'll give it to the guy who charges $500 and charge you more"
3-400 is very roughly standard. The cost goes up if you're using stainless steel frets, if the fingerboard has binding, etc. 
If you know the owner of the place that does it for 550, maybe see if you can get a bit of a discount. I would be very wary of a $200 refret, a really bad one can mess up your guitar, and you may end up paying someone else even more just to fix it afterwards. 
#3
Call Gary Brawer in San Francisco and ask. He's likely fairly high, but there's absolutely no issue about the job he does (and your guitar will be returned PLEK'd in the process). At least you'll have a solid starting point at the high end. 

Like Roc8995, I think we're looking at a $900 price being store profit on top of shipping the guitar out to someone who does a good job. $200 sounds like the job will produce a chipped up fretboard and crapped-up binding and barely crowned frets and.... you get the idea.  It matters because you can end up with a messed up guitar and the need to redo it. 

Honestly, I'd stay away from the "big music stores" for something like this. That's not what they do. 
#4
It depends on the finger board as to price , Rosewood is cheapest and Maple is most expensive, prices around here start at 250.00 for rosewood and 400.00 to 500.00 on Maple