I buy all the John Lewis nicer stuff for the year ahead in the January sales, then I'll buy supermarket (usually Tu at 25% off) at points throughout the year as it's needed/will be needed soon for preschool and childminder clothes. I also pick up odd bits at nearly new sales, but that gets less as she's grown as I struggle to find nice items in good nick now. As a baby I bought everything sale or 2nd hand (eBay, Facebook selling sites, and nearly new sales), with about 60% being second hand.
I spent about £350 in the sales for DD1 (she'll be going into 3-4 next), although that includes a decent winter coat and gillet, and will likely spend another £150 over the year at the supermarkets in T-shirts, hoodie, joggers, tights, socks etc. It's a lot, but I want to be able to pass on as much as possible to DD2, so to me it's worth paying a bit more for decent stuff. It's worked well as I can count on my fingers the number of items I've bought DD2 (about to go into her 5th size of clothes), and of those items 2 were newborn grows as I felt bad she had nothing new, and most others were things in the sale which were just too cute to not buy. Anything left in useable condition once both DDs have grown out of them is sold, which has been most of it, and the nicer brands fetch a much higher price.
Shoes are obviously not included in that budget. I stick my head in the sand on the cost of those. DD1 has flippers for feet and is always outgrowing her shoes. She has trainers and wellies in each size she goes into, plus either crocs or furry boots depending on the season. I save money on shoes by buying wellies in the sales ahead of time, crocs are second hand on eBay, and furry boots are new on eBay. Trainers on the other hand, there seems to be no escaping the extortionate cost. I've tried buying size ups in the sales, but they rarely have the size I want in a style that isn't totally fugly or impractical.