Option 1: Do it yourself
If you are confident in your abilities and have the right tools, you can try to unstick the trumpet valve yourself. This can be done by gently tapping the valve with a mallet, using a valve oil, or using a valve cleaning tool. The cost of doing it yourself is typically minimal, as you will only need to purchase the necessary tools (if you don't already have them).
Option 2: Take it to a music shop
If you are not comfortable unsticking the trumpet valve yourself, you can take it to a music shop. A music shop will typically have the tools and experience necessary to quickly and easily unstick the valve. The cost of taking your trumpet to a music shop can vary, so it is best to call around for prices before you make a decision.
Option 3: Send it to a repair shop
If the trumpet valve is stuck due to a more serious issue, you may need to send the instrument to a repair shop. A repair shop will be able to diagnose the issue and make the necessary repairs. The cost of sending your trumpet to a repair shop can vary, so it is best to get a quote before you send the instrument in.
The cost of unsticking a trumpet valve can vary depending on the method you choose. If you do it yourself, the cost will be minimal. If you take it to a music shop, the cost will likely be higher, but it will be less expensive than sending the instrument to a repair shop. The best option for you will depend on your budget, comfort level, and the severity of the issue.