Well, you're in grownup territory, so pants are expensive. The best "close enough" pants are widely considered to be LL Bean dress chinos, pleated, in dark khaki. But they're $64, not including shipping.
So I'd suggest taking some Indy pics with you to the local thrift store and just shopping around. Pants that are a bit beaten up would be perfect for your needs. (Nothing I hate more than a neat, spiffy, fresh of the rack Indy -- and someone wanting to keep their expensive gear pristine. Gotta get it dirty if you want it to look right.)
To aid you in your numerous searches (as you've asked about this kind of stuff numerous times), check out this page over at IndyLounge:
http://indylounge.proboards.com/index.cgi?board=wherebuy&action=display&thread=2138
A bunch of dead links, but it will point you in the right direction.
And this one at IndyGear:
http://www.indygear.com/
Good info and pics here to help you get your look spot on.