I think I'm the MRI King of Switzerland...... I've had quite a few of these things.

OK, so
a) You must go to a doctor for a referral
You can't just decide to go yourself, and the cost is hideous, so you have to ensure you have your insurance up to date.
Different MRI places are preferred by different GP's depending on what the problem is you have. There are a number of venues for these things, either Stadelhoffen, Paradaplatz, or Balgrist, but best you let your GP decide on where you should go.
As for the cost, this again will depend on your insurance. Some accident covers will pay for all, but if it's an 'illness' you will still have a deductible that you are first liable for...... each insurance cover will be different so your overall cost will depend on what cover you have.

b) there is no option b.