There are many things you can do.
- find a cake supply shop in your area where you can rent pans so you don't have to own every shape.
- for a square wedding cake recently I used my one 12 inch square pan for the largest layer and a 10x15 rectangular pan for the 6, 8 and 10 inch tiers. I needed to cakes per tier so that meant less waste.
- As for piping supplies, I did not start out with a kit of tips. Instead, I bought an empty box, asked what the main ones I needed were and then just bought new ones as I needed them. They are individually inexpensive and I built up quite a collection in no time.
- I found buying a few couplers, and disposable bags in bulk, better than investing in reusable bags, though I do have several of them now.
- for colours, buy your basic paste or gel colours and check on the Wilton or other sites for ratios to mix them to make other colours - then they don't dry out when you keep buying a new colour or shade.
- I have found that online wholesalers, even with their shipping fees, are better for buying fondant. Some of their house brands are just as good (or better) than the popular brands and cheaper.
Hope that helps a bit.