Left wing/right wing, cock feather in/out, it makes no difference if your bow is well tuned to the arrow. If you are a knuckle shooter as I am there can be contact with the hand (not the bow side plate or shelf) with both right and left wing but it is so slight that with feathers it will not effect arrow flight or be uncomfortable. Vanes is another story. With an elevated rest even vanes can be used with well tuned equipment, which should be a good indication that feathers/vanes do not (should not) contact the bow. Shooting vanes off your knuckle can be a bit painful and destroy good arrow flight.
I have no idea why one wing might be more available or expensive than the other these days. The way the birds are bred and raised today they can't even walk much less fly, so no need for clipping. 10 or 12 years ago I bought several thousand full length feathers, both left and right, and availability/price of both right and left were the same then.