You can't train a dog to alert. It's something they have to figure out on their own, and then you train them a particular appropriate signal to let you know what they have detected.
What you *can* train is seizure response work. These are tasks that a dog is trained to perform to assist you and keep you safe during and after a seizure. These tasks can include keeping you away from things that might hurt you during a seizure, clearing your airway to keep you from choking if you tend to vomit during a seizure, and using a special kind of telephone that automatically dials emergency services using a big button that a dog can trigger using its nose or paw.
Training this kind of work can be more difficult and expensive than other kinds of service dogs, because the dog has to remember what to do, and do it reliably, without being given a command. A guide dog for a blind person is told by its handler to go left, right, or forward. A service dog for a person in a wheelchair is told to pick up a dropped object, or perhaps to trigger an electronic door opener. But, a person having a seizure, or often even after a seizure, is not in any shape to command or control a dog. These dogs have to be even more sure of what they are doing, and less likely to misbehave and need correction than most other kinds of service dogs. So, if the trainer you are considering is charging thousands of dollars, they are well within the industry standard for estimating the cost of training.
Most reputable service dog organizations will help you with fundraising. Have you contacted your local Lions Club? They are a community organization that often helps people with disabilities raise funds for medical equipment and assistive devices, including service dogs.