Heck of a project...
It would be great if you could hunt it at your leisure.
Distance and time though.....
IF I was intent on searching that big a sight I'd be tempted to choose the best time of year. Just past winter , whatever winter is in your state , l.o.l..
Or at least when grass and weeds are at thier lowest point and temps are below human flesh melting.
Then approach the site with as big a group of experienced (at rings ect.) detectorists for a group hunt. IF permissible by those who enforce right of way activities rules.
Have a get together potluck or something after.
A permissioned approach vs risking getting run off could be to get approval and perhaps sandwich coupons or something from the outfit that maintains / mows the right of way.
Collecting junk and bagging it for pickup can really reduce mower blade and tire damage. (!)
(As kids we used to do cleanups for a utility company. Church group or scouts or something.)
A volunteer group going ahead of the detecting group cleaning up could help reduce trash . They might find more guns and bodies first. Not always a bad thing.
Too far a run for me , your offered distance from your home.
No problem asking for expenses being covered if it's not in your ability or interest to spend so much time wear and money.
Not an insult. Just how it is.