A 46-463 is the bed extension accessory alone for a 46-460 lathe. $800 for a bed extension alone for a midi-lathe would be a rather spendy.
I suspect what you are looking at is a 46-460 with the 46-463 bed extension accessory.
For the combination, $800 might be a reasonable price for a new machine, but it would be a bit high for used equipment.
The Delta 46-460 is a fundamentally a good lathe, but it has garnered a less than stellar reputation because the ownership of the Delta name has changed hands several times in recent year. Unfortunately, responsibility for spare and renewal parts for Delta tools has not always followed ownership of the new tool brand - and what this means is that it can be difficult to find replacement parts for older machines.