You can take the DTPC tourist boat cruise that runs between Alappuzha and Kollam and back. It leaves each town daily from the DTPC jetty at 10:30am and costs Rs300. It is a big boat and doesn’t really go in the backwaters but on a pretty wide canal and for some time on a lake. It takes 8 hours and they can be pretty long. I did this just a few weeks ago from Kollam to Alappuzha but did get off halfway at the Matha Amrithanandamayi ashram and took the bus from there.
From Alappuzha you can take a bus to Karungapally, then another one to the ashram. There you can get on the boat which should get there at around 2pm but you should ask at the DTPC office to confirm this. The boat ride from Kollam to the ashram was Rs100 and the buses Rs30+8. This way you still spend 4 hours on the boat, and I think that is enough. You could also take the boat from Alappuzha to the ashram and then the bus to Karungapally and on to Kollam. I don’t know which half of the boat ride is the better one.
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