It sounds like you're off to a great start. You don't need many toys to be Waldorf. But going Waldorf on a budget can definitely be done. I've done it has have many other mamas here. Some ideas
playsilks- join a co-op for Dharma Trading and buy some various size silks and dye them yourself using kool-aid
-check out the local thrift stores for silk scarves or scarfs of various textures and colors
-a really large scarf or even sheet makes a great start of a fort
play kitchen items- I agree with the pp also We have had great luck with buying an assortment of small stainless steel, enamel and wood dishes/utensils/pots and pans etc from thrift stores and garage sales
books- I am constantly scouring the thrift stores and garage sales for cheap books about the different seasons, it only takes a few good books for a seasonal nature basket
I personally would weed out the tv show based books like Disney etc, though there are some character's who started out as books.
stacking toys- these are not a necessity but if you really want some ours do get a lot of play and are very open ended. We have some Spiel and Holz ones which are really great but some wonderful mamas make some cheaper versions on Etsy.
Nature items- great b/c they are free
We have a basket of seashells and river rocks and such that are pretty unbreakable so I don't have to worry about ds coming home. Pinecones are great too.
A nature table is really great- you can add items out of nature or little toys you have around the house that are seasonally related.
Scour your local thrift stores and garage sales and be open mined- I always find great wooden toys and other items that potentially make great toys. For example we have two bread box's for ds a wooden one (makes a great barn, house etc) and a metal one (makes a great garage, fire house etc)
I would also check out the playroom thread here and also the Flickr thread for some great ideas.
ooh gotta go ds is begging me for a shower so we can go out in the car, lol.