It sounds like you have a wellness plan with one of the big companies. I prefer small local clinics with vets I know and trust. I have had the same vets for over 20 years.
Here vaccines can be obtained through mobile clinics for under $20 a shot. Vets charge $25 to $30 for the major vaccines, but require an annual exam. Since your cat is indoor-outdoor, you need to have the FVRCP and the rabies vaccines. These days, the rabies series is two shots, one year apart, then the shot every three years. The FVRCP us a 3 shot kitten series, followed by an annual shot. At some point, those shots get more space between them. The feline leukemia series is something to discuss with the vet. There are some risks with that.
At her age, exams could be annual, as long as you examine her regularly yourself. If she goes outside, there are many more bad things that can happen to her, so you do need to look her over her regularly. Vet exams pick up early signs of problems such as tooth decay and kidney issues. Microchipping is a good way to insure she gets back to you if she gets lost. That's especially true if she were to end up in a shelter. A simple scan, and you get a phone call.
Can't comment on the heartworm preventative, because we don't see that in cats here. Frontline Plus flea prevention can be purchased from Amazon or Costco at a reasonable price. It may not be necessary in the winter because fleas die off then, especially in colder climates.
The cheapest way to keep a cat healthy is to keep her indoors and feed her high quality food. You only need the FVRCP vaccine and the risk of her getting sick or injured is much smaller.