What is needed if the pump is "sound" i. e. it operates well, starts right off and you haven't run gasoline through it, is a reseal (all seals, O rings etc,) and springs (the plate return and breakover spring, governor spring ). And the throttle shaft/bushing.
This will cost you about anywhere from 160. 00 (if you do it yourself) to $300-$400 for an injection pump shop. Plus they calibrate it.
If you are paying the $700+ that is a reman pump. A reman pump will contain some new items and some used items, calibrated to OE specs. It will be essentially the same as having yours tuned up/resealed. Your pump is a core only.
A rebuilt pump, costing $1,000. 00+ would contain the new hard parts such as the hydraulic head, governor assy, possibly a new shaft and/or vane pump along with timing advance, overflow valve KSB, shut-down solenoid etc. like new but with minimal used parts.
I'm not ranting... . I simply like to know what I'm getting, and with the reman pump on exchange, you will not know. I would ask for a list of hard parts replaced on the reman unit. Act like you know just as much as they do. They will be stumped and give you the information sheepishly or possibly not... ... ... ... . WE will coach you on this if you need assistance.
Let us know what (new) parts you are getting with your reman pump. I'd personally request that you have YOUR pump taken down to the last screw, inspected and resealed with the items I mentioned above. There isn't any sense in paying for a reman and getting used items back when you already have used items. If you pump isn't worn out per a pump flow test, get that thing reselaed.