The problem I having is the fact that CHDK builds only work with certain firmware versions and if I buy a new or used camera how can I know that the one im getting has comatible firmware installed?
But if you are buying used - have them send you a "sample" picture and then use the ACID utility to identify the firmware version and see if its supported.
And recently, the various CHDK supporters have been porting new firmware versions and cameras for anyone who asks nicely. No guarantees of coarse - this is an all-volunteer effort.
Can someone suggest some camera models that are likely to ship with comatible firmware?
There are probably lots. All three of my cameras have CHDK for every know f/w release for example. I'm sure you will get other comments.