Tough to give an estimate for a Model 28 that has been modified that much. You didn't mention the dash no. (i.e. Model 28, 28-2?), serial no., or the barrel length (4" or 6"), and all of those details could affect the value. A 4" bbl. version is generally worth a little more, and early S-prefix Model 28s are too. A non-factory nickel plating job generally decreases the value significantly, especially if the cylinder is not well done. Also, it's not wearing checkered magna stocks with which it would probably have shipped. However, nice checkered target stocks have a value of their own depending upon which type they are. If it's an early S-prefix 4" HP, $600 may be a reasonable price. If it's a 6" bbl. later model, perhaps $450-$500...almost any decent N-frame revolver is worth $500+ if the condition is good. A couple of pics would help greatly, as would some additional information. Good luck!