Oxbow is another commonly found pellet, but KMS is still cheaper by far while still being a quality pellet. I wouldn't take on pets if I did not have the funds to provide for their needs.
You'll find Kleenmama comparable to Oxbow or Sweet Meadow. The shipping may be expensive, but did you look at how cheap the pellets are? Waaayy cheaper than anything in the pet store.
Besides, how expensive can they be? Do you have a lot of guinea pigs? I split a 25 pound bag with a neighbor, and my pellet cost for my two pigs is about $19.25 every 6-7 months. That's less than $4 a month, and I use Kleenmama, and have to pay for 2,000+ miles of shipping.
Keep in mind that the OP may be in a different country. I know to get 20lbs of KMS pellets to me it costs over 65 dollars (on top of the pellets) that works out to $80 ish. That's $4 per pound, I can buy Oxbow (50 lbs) online for $112 from a company in eastern Canada. Which works out to be $2.24 and it lasts 11 months.
So don't slack her for wanting to buy something cheaper. I personally understand not buying KMS.