1999 focus wifey got stranded at tescos, took out spare key and it started, so basicly presume the chip in the key has died

thing is its the main key with the remote locking buttons so she doesnt really want to use the spare, havent opened the key to look for the chip yet

so whats the cheapest way to resolve this can i buy another chip for the key and have the chip recoded by one of these locksmiths? they all seem to do fords etc now

can they read from the good key and program the new chip?

or do i have to buy a whole new blank key and have it cut and coded?

any advice?