Given your budget, I would consider a couple of options. A Springfield Armory GI can be had for under $500, if you look around. The ambi safety can be added for the cost of the safety ($25 -$50) and fitting it by a competent pistolsmith.
The other option would be to find a used pistol that has one fitted for that price. Might show wear, but it will when you carry it. I have seen several over the years on Gunsamerica, AuctionArms, etc.
dclark