Did you know that you can apply for a MAC Pro card? So you can receive discount. This may be a good option if you love MAC but are concerned about the cost. In my kit, I have a selection of brands-all high end and professional. When I started out, to keep costs down, I bought a small selection of shades in light and darker foundations, and mixed them to create other shades. Once working with clients you will soon find what shades tend to be more popular and what you need to add more of to your kit.
Also, Artdeco do a great range of make-up, and you can get a good little kit together from them.
You could also add a couple of MAC products to your Artdeco kit, and add on more MAC products as you earn.