Looking at several websites including the Halcyon website, Scuba.com, Leisurepro, and Scubatoys (the last three being actual online sites I have purchased gear) I found that when you add up the components it can get quite expensive. I found a harness system for $60, a pack plate for about $71 but most were at least $100 or more, and a wing for $300. All total it came to about $431. The average cost I would say for a back plate with wing would more likely run around $580 which would be $130 for the harness, $150 for the back plate, and $300 for the wing. And then I would also have to use a weight belt.
I found an Aqualung Zuma travel BC on sale for $299. I also found a Dive Rite travel back plate with harness on sale for $399. So the back plate with wing set up was still $100 more than an off the shelf back inflate BC.