Don't rule out other soft luggage, as they all mount pretty much the same way, with straps. The only consideration would be the length of the straps. Make sure the will fit the Burgman, as the seat is wider than most bikes. The GIVI T411's work well for me. Many also choose Nelson Rigg. Cost can vary, but $50-150 is in the ballpark. I paid $100 5 years ago.
This may also help