The cost of building a pet mobile app can vary widely depending on complexity. A basic app with features like pet information might cost around $20,000-$35,000. More complex apps with features like appointment booking or chat with vets can range from $37,000 to $60,000. The most expensive apps, with features like video calling and e-commerce, can reach over $100,000. Remember, this is just an estimate and the final cost can be influenced by factors like developer location and the number of platforms (Android/iOS) you want to build for.