P220 is single-stack .45 ACP. Slide diminsions are the same as P226.
P225 is single-stack, (sorta) compact 9mm.
P226 is a full-size 9mm, .40, .357SIG with double-stack hi-capacity magazine. This is the flagship pistol, and considered by many to be one of the best military/law enforcement sidearms of all time.
P228 & P229 are newer, slightly more compact handguns. Hi-capacity magazine.
P232 is a compact .380ACP styled much like the Walther PPK.
P239 is compact, single-stack. Improvement over P225 as compact pistol.
There are so many variants now of the P226, so I'm not sure which one you're looking at that is priced twice as much as the others. As used guns the availability and popularity will have an impact on price.
When it comes to Sig Pistols there is nothing to compare them to. Great design, great feel, great balance, WHAT else can I say but they are a great addition to anyones collection or for a 1st time buyer. IF you are looking to carry the P229 is a great balance of size/weight/capacity.
+ 1 on the Sig 226 great gun mine has Probably 7,000 to 8,000 rounds through it not 1 issue ever. How often do you plan on carrying it? If you are going to carry it alot i would consider the 229 if it will be used for home defense more i would pick the 229 no doubt.