I went through the same issue, and when I eventually DID find an excellent opti-coat installer he couldn't book me until August. It's a shame too because he was going to charge me just $250, and this is a guy that has a detailing school and does work for BMW, so highly experienced. Since I couldn't do the wait without some added protection, I ended up going with a similar product from Wolf's Chemical called Hard Body. I've found that as long as you take your time, read the directions and use a little common sense, you can do many of these things yourself. Yes time is money and this is why the installers ask for so much money, however $600 is a little steep. Since the FRS/BRZ are relatively small cars, they don't take much time to do. You'll spend the bulk of your time doing prep work, polishing, etc.
end result:
does have a few swirls here and there, but they are visible only in certain lighting conditions. Swirls are inevitable anyway if this is your daily driver. I'm sure i'll have to re-apply the sealant next year or so.