Chewy? Or Stokes?

My baby girl Ruby was just diagnosed with FIP, after I waited 5 days to take ger to the vet because I thought it was just gas. Ruby is fully grown and only weighed 4.5 pounds before she got FIP. So seeing her bloated after eating was a normal occurrence. But after 5 days I toom ger in because I knew something wasn't right. She was diagnosed with FIP. My vet recommended GS-441524 medication for her. So I looked it up and the pharmacies I found are Chewy and Stokes. The problem is Stokes cost like 1800 dollars for 30 doses. And Chewy only costs 150 for 30 doses, so only 450 dollars for an entire round of it. That's a massive price difference. One I can afford and one I can't. So, which one do I use? Has anyone used the Chewy version and their baby got better? Is one better than the other? Is one gauging their prices to take advantage of desperate pet parents? I am distraught and terrified because I waited 5 days to take her in and I know this disease can kill rapidly. So please, please any help at all will be greatly appreciated.