You're looking at 600-1000 dollars to be replaced professionally. 200-500 on your own, this will show. and maybe 40 bucks to refurbish what you got. However, the refurbish, you may not get handles that match or fit right given the age. The cartridges or valve bodies should be available. Make sure to match them up. Also seats in the bottom, inspect nad ensure they are good. No chips or broken. Inspecting the valves themselves can give clues to their condition. If there the rubber is destroyed on the bottom of the valve body I would highly consider changing them. The metal seat on the valve can come into contact with the seat and damage it. Typical if it was not maintained.

In my honest opinion, a delta r10000 rough in with the bigger plate to cover the holes. Turns 3 handles into a single. Makes everything easier going forward and lifetime delta carts replacement which is nice. That is the 500-1000 dollar Cad range. Maybe less in the US, still labour can be 3-5 hours on something like this plus materials. This will cost the most, but will make the shower much nicer, easier to use and will also have a thermostatic mixing valve. But it costs a heck of a lot more. So yeaaaah, refurbish or pony up. I would HIGHLY recommend hiring a professional for a fresh instal.. Not saying you can't do it, but leaks behind the wall are expensive......

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EDIT: Change rough in, had R220000, which is over kill, just needs the r10000