Have you considered an aftermarket fairing like quadzilla? I think those mount directly to the windshield mounts and you don't need to change your gauges. I'd think if you wanted to mount a Harley batwing, you'd have to change your tank dash to remove the speedo, change the headlight mount, and probably a lot of other things.
Have you picked out which one you want assuming you are going aftermarket.
I would think they would have a list of included or extra turn signal relocation brackets etc when you pull up the installation instructions or their tech line could tell you what you want to know.
Well, with an Ultra or Street Glide you are stuck with the fairing. On a hot summer day I can pull the bat wing off quicker than you can say "lets ride!"...
If you want a loaded fairing with gauges, radio and all then yes, look at a new bike. If you just want a fairing for foul weather than a clip on is the way to go. After market will set you back around a grand if painted. I found a used beat outer shell from a Electra Glide. Made my own mounts to fit the stock windshield mounting points and did my own paint. I have about a buck and a half in mine.