To me it sounds like you are after an incident + spot metering. Most of these meters will be able to handle flash.
Something like Sekonic L-358 with spot metering attachment should do. Depending on condition you should be able to get it for around $200-250 (without the attachment).
Another more bulky option would be something like a minolta meter + pentax spot meter. But that will add a lot of bulk having 2 meters around.
Another option is Sekonic L-508, L-608 or L-558 (it's pretty much the same as the latest L-758).