about £4 to £6.00 pound depends where you come from mainly i would not advise cutting them urself because guinea pigs have a vessel in there nails which if cut wrong could bleed and get infected.
u can also get them 4 free look in the newspaper they breed really fast and people sometimes don't want them they're usually free or really cheap =) They cost around 20-100 dollars, but u can...
Just go to you tube and type in how to properly cut your guinea pig's nails or go to instructables.com or on goggle web or video. Thank you for that wonderful question! P.S: You'll need human nail...