I've used spentrade on eBay for some barriers, bought a pallet of new oxfords and some second hand JSP navigator all for a recent TM job I did.
Cones - Buy new, not worth buying second hand will have missing sleeves and all sorts, i prefer one piece rubber cones personally.
Signs - What do you need, could go down the Q Fit frames and pop on and off with the toggles (I zip tie the toggle to stop the plates being nicked) Metal frames and Zintec plates are cheap enough, but you need to get them riveted (rivet all mine in an attempt to stop them booting them through) alternatively there is the plastic ones, not used them myself, seem fragile but can get a weight block from them - Spentrade has loads.
Sand bags - buy pre filled, best thing I ever did, the pain in filling them is not worth it and as others have said, you will go through them, people carry them off, drag frames around shredding them to pieces and pouring them out.
All takes up a lot of space when you got a bit to store (Wife can tell you that, as half of it is in the garden)