I've resuscitated several of bent rims and reinstated them for beater duty. My approach is to tape the spokes together at the cross, then remove the rim from the spokes completely. Hold against flat surface to determine where the bends are. If a sturdy work bench is available, I'll clamp the "flat" section of the rim to the table, with the bent overhanging the edge, then lean on it - heavily.
W/o sturdy bench I'll determine the high spots, then lay the rim on the floor with the high spots resting on a broom handle, hockey stick a pair of wooden blocks or whatever, then step on the rim. Sometimes I have to inch my feet towards the blocked up section to get a strong enough bend into the rim to straighten it out. Repeat until good enough or alotted time for the project runs out, relace rim into wheel, tension, true and ride.

This is at disassembly, something like 17 mm out.


This is after 1st round of bending, something like 11 mm remaining. Not good enough yet but a big improvement.


For some reason I didn't follow through on the photo shoot, I think I had to call it quits for that evening or something.
Anyhow, at the next session I got it down to abt 2 mm deflection, at which point it went back into the wheel.
So maybe I wouldn't/haven't taken it on a cost-to-coast tour, but it's so far it's doing fine.

I've never had much luck tackling serious bends with the rim still in the wheel, IME the opposite spokes won't allow for enough of a counter-bend to end up anywhere near to straight. I've had good results pushing out low spots with the rim still attached though.

Either way, it still a good hour's work or so. 20 minutes to secure the spokes and unscrew the nipples, 10 minutes of bending, and 30 minutes of reassembling the wheel. For me, that'd go a long way towards simply replacing the rim or building a new wheel from scratch.
If you have to pay someone for the time, this'll buy you a new budget wheel from the LBS.