For the most part, my son (now 4) went barefoot in the summer or just wore gripper socks for warmth in the winter. It's the best for your feet! Of course, there are many times as a toddler gets more active, walking more and being carried less, that shoes are a necessity!
We always - and still to this day - buy year-round converse and vans canvas sneakers from Zappos (LOVE ZAPPOS!) and summer sandals from Target. I know that the expensive shoes are great and don't wear out, but seriously, how much wearing out can a 20 month old do before they grow out of them?
Even now, I am still buying a complete new set of shoes every summer/winter b/c his size has changed. So I spend about $130 annually for brown and blue sandals; flip flops; brown (or green), blue and black sneakers; slippers; and shoes for soccer. I almost always get the same ones or similar, just the next size up. Unless you are saving them for the next child, I think any shoes over $20 for a kid is way too pricey.
My mom sometimes buys a pair for him at Payless. We don't wear leather and they have a lot of synthetic/cruelty-free options at a good prices that of course he never wears long enough to wear out.