Hey sheep dog, dont loose any sleep over it. Better than kicking yourself down the line. M-28 rear sights are not cheap and those holes would have bugged the **** out of you. You did right, walk.
I bought a perfect Model 28 rear sight on eBay about a year ago for $28. Everybody has their personal limit on the value of things so a deal for one guy is extravagant for another.
I do NOT buy modified guns. IMHO you did NOT mess up! Modified guns often turn out to be a problem and become money pits. Get one that is still to factory spec's. They are still out there.