You do not need to join GoodRx to use their coupons. Anyone can obtain a coupon on their website. Use this link and you should be able to set your location so you can compare prices between local pharmacies in your area:
https://www.goodrx.com/insulin-glargine?dosage=five-3ml-prefilled-pens-of-100-units-ml&form=carton&label_override=insulin glargine&quantity=1
Keep in mind that some pharmacies have a pet restriction with GoodRx and will have a higher price if the prescription is for a pet. In those cases, GoodRx will pop up asking if the prescription is for a pet and will route you to a different coupon for pet prescriptions at that pharmacy. As far as I know, Rite Aid does not have this restriction and the $90 price is for both human and pet prescriptions.
It seems a little bit too good to be true, but I just noticed GoodRx is currently quoting a box of 5 pens of Insulin Glargine at Kroger Pharmacy for $22. This seems incredibly cheap but its worth looking into if you have a Kroger Pharmacy near you.