Yup, normally pressed up together, maybe on splines.
New seal probably in the £10 to £20 retail range if it can be got at all. Motorcycle ones are commonly found as spare parts but car ones will take bit more finding. I imagine suppliers are geared to the hundreds and thousands a month trade sale market not individuals.
Hafta change the outer seal too to keep crap out of the bearing. You'd need to be very sure of bearing condition too if you were going to re-use it. The serpentine belt puts hefty side load on it.
Doesn't seem economic when £40 - £60 gets a half decent new unit good for 50,000 + miles. After all changing a pump you put on yourself is only a couple of hours work if you have the tools and took the time to do the extra stuff to make it easy next time round. DIY reconditioning water pumps is another job life has got too short for.