It is a long drive in a minibus, but there will be no other options, IMO. Or local bus yet this one is takes even longer.
Buses are often not much slower than shuttles and are of course much cheaper. By shuttle it is 5 to 6.5 hours (depending on pick-up point). We went from Sierpe to San Jose by bus. First a bus (30 minutes) from Sierpe to Palmar Norte (but a taxi works too) and then a Tracopa bus (5 hours) from Palmar Norte to San Jose. So from San Jose a Tracopa bus to Palmar Norte and then a bus or taxi to Sierpe. But I see Tracopa also has one direct bus from San Jose to Sierpe at 8:30 am. The Bug Lady's website also mentions Tracopa, by the way.