I checked it out and this does indeed look like a way to go:

transfer from airport to Sapporo City 2 pax 15,000 yen
5 pax 18,000 yen
airport to Otaru 2 pax 18,000 yen

They have different size vehicles with commensurate differences in fare up 50+ bus.
Today the exchange rate is $145 for 15,000 yen and $175 for 18,000.
Thanks, Ngaire.
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Helen