Hello,
I'm assuming that your friend wants to develop her own film rather than get it processed elsewhere which will be expensive. Probably about the cheapest is to go for some Agfa Rodinal. Her local Jessops may have some, or they can order it for her. It'll cost about 9 pounds and by buying it locally she'll save on postage. Then she can use the 1+50 dilution for economy. She can use water instead of a stop bath.
Another alternative would be to use ID-11 at a dilution of 1+3. That gives nice tonality, however the Rodinal will be cheaper and the concentrate lasts forever.
Hope that helps
Mike