I was faced with the same situation a couple of months ago with my SA GI Champion. The problem is that the front sight needs to be ground out and a dovetail needs to be cut into the slide. I had picked out a set of 3 dot sights for $39. The estimate from my gunsmith for the machine work was $120. Add that to the sights and I was looking at a $159 investment.
I had purchased the gun 6 months before for $400. This would put me at $559 for a 4" 1911 base model with new sights. The gun shop assured me I could get $425 for it at a gun show and they would consign it. They got the $425 and only charged me $25 for the consignment fee. I put the $400 down on a new Kimber Custom TLE with night sights for $700. So, for a $150 more investment this moved me up to a semi-custom high end gun with match grade components, 3 dot night sights and many other features. It was well worth the price.
Good luck with your decision.