The Ruger .22/45 is based on the dimensions of the 1911.
I have two of them.
One has at least 50,000 rounds on it. Maybe twice that. I really lost track.
I bought the second one just in case the first one died...
I also have a Ciener .22 conversion that fits both my full sized Kimbers.
The conversion is ok, but, I really don't think it would hold up to a tenth of the number of rounds of the Ruger.
It's more of a novelty to me than anything else.
An alternative to a .22 would be to invest in a reloading setup.
The .45acp is an extremely easy and friendly cartridge to reload.
It's no problem at all to get 10 or more uses out of the brass.
People dog on Lee reloading equipment all the time, but, my Lee turret press is 35 years old and still going strong.
This press:
http://leeprecision.com/reloader-press.html
is pretty much all you really need for the .45acp. due to the low operating pressure of the .45acp.
It's very possible to get into reloading for ~ half your .22 budget.
It's something to consider...