Well, keep in mind that CMC is one of five colleges smushed together in one town. I don’t think you’d have to worry about finding your crowd there – having five schools means there are enough students there who will have interests like yours.
Mudd obviously is a very strong school for Engineering and it’s right there in Claremont. You would have three years at Claremont McKenna to build connections with Mudd, become familiar with its campus, etc. That would make the transition far easier than if you had to move cross-state or cross-country.
It sounds to me as if the academic path – in terms of finishing up with Engineering – is clearer at CMC/Mudd, while the $$ part is clearer at UCSD, since you do not know what kind of aid you will get at your Engineering school.
So – check with Mudd and other Engineering options you would be interested in if you did the CMC 3/2 program. Ask them if they follow their regular formula for granting aid or if it’s different for a 4th- and 5th-year student.
Also check UCSD – if you can, find out what percentage of non-Eng admits eventually are able to transfer into Engineering.
If the financial aid for the last two years of the CMC 3/2 program probably wouldn’t be a problem, that’s a boost for CMC.
And if it seems you’d have a fair opportunity to transfer into the Eng school at UCSD, it’s bonus points for UCSD.