It would appear that you are in the information gathering state and currently reluctant to work directly with a Realtor. Quite frankly, I think the only way you will achieve due diligence is by getting all the fact. So when the time is right, please contact me or another real estate professional.
You can search for Rossmoor listings here at http://www.mlsfinder.com/ca_ccar/vickienagy
Here is a list of Rossmoor properties listed that are priced up to $475,000. There are 99 properties.
I did run a list of Rossmoor homes that have ownership type listed as co-op and here is the link to them.
(Obviously these are the homes you are trying to avoid) Be aware that the MLS data is not always accurate. There may be some co-ops that aren't tagged as co-op in the MLS.
Keller Williams Realty
$7,000 Golden Rain Foundation one time membership fee
Not sure if you mean fiscal/budgetary requirements for the project itself, or financial requirements for obtaining a loan on any property. If you're seeking answers on the latter, I am happy to help.
Rossmoor is confusing at first with some of the units condos and others coops. I would be happy to provide you with any or all the current Rossmoor listings and discuss the fiscal requirements offline. Please contact me if you would like to receive them.