I'd ask you what you're looking to accomplish with the swap? If commonality is important to you, I'd stick with the two compact sizes guns and keep the 228 and M11 and shoot the shit out of them. The 226 handles, loads and shoots enough differently for *me* that I prefer to be dedicated to one or the other. Granted that comes from a "whittling on the minutae" perspective.
Re just the price? It's on the edge of doable, IMO. The reason I say that is one can find REALLY good deals on older trade-in stamped slide Sigs if you're patient and know where to look. In particular if you're willing to convert them over to DA/SA from a DAK system. I've purchased multiples in the $400-450 range, FWIW. Given the price point on the newer Sigs, I think you could probably do a bit better than the mentioned deal. Unless of course you just want out of the M11A1.
Just 2 pesos.