Stain or paint grade? Assume this is interior. Not much variation in doors for interior use.
You may be asking about pre hung. That's a can of worms. 2 Doors, hardware, jamb material plus casing can't be more than $600.
Looking online it seems that buying a 'book' door is something no one considers or knows about. You go to a lumber yard and order a door or 3. "Book" means it's a door, no prep, just a door out of the rack.
Manufacturers like Simpson have made the classic
1510 door for ages. They must make 30 designs, all iterations of pretty much the standard. 1510's are in stock at most decent lumber yards in sizes of 24, 28, 32 and 36". An arch top could take weeks or months to get. Should be under 200 ea. So no need to even order.
Expanding an opening is another thing altogether. Pocket doors take 2wice the width in terms of the required header. So a set of door's 4' in total will take around a 9 foot header measuring the header end to end.
Having a 4 foot set with an active door and an inactive door pinned most of the time for the active to have something to latch to means you get to use a about 23" of walking space every day. The only doors that both swing open simultaneously are in movies. No one actually behaves like that.
Minimum for me inside is 30" each.
A decent door hanger here in CA would charge $500 to assemble a jamb, install in an existing rough opening, and install hardware and trim. If you can find a door hanger. The painter would be about the same over the course of 2 days if he is local and can get to another job during that period. If not, then 2 days pay which here is $300/day. For anyone that I would let paint anyway.
Rough opening is anyone's guess. 30 years ago I got $1000 for a RO patched in and did a few a month. I'm guessing 2K these days no electrical. There is always electrical.
I hate anything prehung. The product never seems to be as good as a good ol' book Simpson fir door.