SP135 raw water pump options

I have a Lehman SP135 in my TC Sundeck. I'm putting together some spares and wanted to include a complete water pump. Somehow I apparently still have the old Jabsco pump that seems to be working fine "for now".
My question is the Jabsco 2C48 pump seems to be priced in the 600/800 range the replacement Johnson pump is in the 500/700 range and a NOS 2C49 on ebay is 100/300.
I don't get it?? Why the huge difference?? Pretty sure the 2C49 will fit and just need to adapt down from 1" ports.
Am I missing something here?? I'm not cheap but I also don't want to waste $$$ for no good reason. Thanks

Our boat has a good working Jabsco and carries a Johnson pump and gear as a back up. This was an easy decision because a non working pump and the boat is then a no go. Plan to install the Johnson pump next spring.