I have had two engined rebuilt, first was my GX it was with one of my old customers so mates rates were involved.
I had first o/s pistons and rings so engine was bored new bearings ,timing chain and I think tensioner,full gasket kit,cam was ground,head was machined and valves were done at the same time,oild pump was also stripped and checked cost to me was 900 bucks.
The same guy did a std A12, bore was hones and new rings fitted,new bearings and timing chain,head was done at the same time also full gasket and seal was fitted cost on that was 500.
shop around and have a list on what you want done.
I was in the trade at that time so I had many contacts believe it helped with my resto.
A12 are not a hard engine to do but with my GX engine getting 1st oversize pistons took a bit of searching
ade