Is the father married to the mother? Otherwise, how can paternity be proven in the eyes of the law? The suspected father would have to agree to genetic testing, and the fetus could only be tested earliest around 10 weeks gestation according to this site:
http://www.paternity-answers.com/patern ... -test.html
How long does the mother want to wait to have the procedure done?
The test itself seems like it would cost way more than an abortion. Seems like you've got an angry grandparent-to-be trying to scare you into being accountable.
Legalities aside, it takes two to make a baby, so perhaps splitting the cost would be most ethical, if abortion is the route both parents agree to.