Pogo stick or space hopper are viable alternatives and a skateboard or heeleys would work if the roads are beautifully tarmaced. I would hate for you to get out of the airport and find a poor road surface, so please check this before packing your scateboard.
if buses are cancelled (for whatever reason) then you would not be the only one trying to get to Pamporovo. See if you can pool resources and share a hire car or get on a coach with another party in exchange for a few quid perhaps!
Find out the Bulgarian for 'anyone going to Pamporovo? I'm happy to contribute to cost' and write it on a board in Bulgarian and English then walk around arrivals hall with board and you never know!