Hi QW, I can just offer my perspective; may not be relative in the states though.
For the sake of 20 bores, I'd consider a contractor.
Getting set up properly and experiencing the challenges of boring can take quite an effort. I've done 5" bores in a couple of hours and had 2" bores take half a day.
Occasionally a rework will show up where another contractor has misaligned their repair and I have to reweld and rebore. Usually this happens from the use of machined cones for alignment, rather than working off known datum points (other pins/bolts or machined surfaces)
In my part of the world, I see secondhand setups for the $20K mark, though a hydraulic unit did pop up recently for $6600. It had been sitting for a few years/didn't have all the tooling/no welding attachment.
I use a Sir Meccanica borer with the welding attachment and run a Lincoln CV320/LN-7. Sometimes I will stick weld a bore; it may be quicker than setting up the MIG and attachment, or if the base metal isn't a 250 grade mild and could harden with MIG welding.
Be sure to let us know what you end up doing.