A divorced Protestant may become Catholic.
If the divorced Protestant remains single, then an annulment is optional. One can be divorced and become Catholic and partake in all the sacraments except marriage and holy orders. If one feels called to marriage or to holy orders after converting, then an annulment must be granted.
Annulment is a complex subject, and it can be even more complex when conversion is involved. Is your friend speaking with someone in her parish? If not, have her talk with someone who is directly involved with annulments. If she has spoken with someone in the parish and is still confused, perhaps she could talk with someone involved with the Tribunal down in your Diocesan Cathedral.
As far as prices go, it can vary by case.