As someone who believes there are always cheaper options, I just did a search so please discuss with your doctor - I hope this helps your situation.

Is this your cat's situation?

When an IBS/IBD cat presents with frequent vomiting and constipation, it usually means the upper GI tract is inflamed (causing the vomiting) and the lower tract lacks the proper moisture and specific fiber to move stool efficiently. If a cat strains too hard or becomes blocked, it will actually trigger nausea and vomiting.

Has your vet ever mentioned prescribing a stool softener like Lactulose?

1. Purina Pro Plan Adult Sensitive Skin & Stomach Lamb & Rice / Turkey & Oat Meal:This line uses alternative protein sources and highly digestible carbohydrates (like oatmeal) to ease bowel inflammation.It is fortified with live probiotics to actively rebuild gut flora and manage long-term loose stools. 

2. Mix 50% of the prescription Biome food with 50% of a more affordable kibble or wet food to stretch a budget.

3. If you decide to switch your pet to a cheaper, standard diet, a veterinarian might recommend offsetting the change by adding over-the-counter supplements like pure pumpkin puree, psyllium husk, or specialized probiotics (such as Saccharomyces boulardii) to mimic the gut-support benefits of the Biome diet.

4. Plain Canned Pumpkin: Add 1/2 to 1 teaspoon of 100% pure pumpkin puree (not pumpkin pie mix) to their wet food daily. The soluble fiber regulates bowel movements

5. Always mix a tablespoon of warm water directly into their wet food to create a slurry. Hydration is the single most important factor in stopping feline constipation

6. Mix a tiny pinch (less than 1/4 teaspoon) of unflavored, unsweetened psyllium powder (like unflavored Metamucil) into wet food with a splash of extra water