If you are only observing ready made commercial permanent slides, then further accessories are not needed. If you want to prepare your own specimens, then you need to invest in slides, cover glasses, mounting media. These are not expensive. A safe working environment, or even a home laboratory costs more, of course.
Obtaining these accessories might not prove to be too easy, however. Chemical companies might be reluctant to sell stains and reagents to private people. I would first try to find appropriate materials from educational supply companies.
I have already written an article about the recommended accessories