There are a total of 15 homes on the active status in the MLS right now. All are in San Mateo, the least expensive property in Belmont is $565k and $625 for San Carlos. I next question that I would need to ask is "Are you looking for a fixer upper?" If move in ready is a requirement than a Condo would be a better idea.
Below is a link to a list of all the properties in San Mateo that are priced between $399k &$520k. 4 of those are regular sales, 4 are Bank Owned(REO's) and the other 7 are Short sale.
I'd be more that happy to help you out, look me up!
San Mateo will most likely be the city of the 3 you mentioned where you may have a chance to purchase a 3 bed/ 2 bath because the homes in Belmont and San Carlos are more expensive. A 2-3 bed/ 1 bath is more likey to be found in San Carlos and Belmont.
Best of luck.
List in San Carlos (3br 2 ba below $500,000)
Nothing in Belmont as of today with all the criterias
You can check on your own at http://realtyfinancial.com
or contact Val at 415-385-8949