I have a pair of boots I bought at Walmart that have lasted all year so far through molten plastic and hydraulic oil ( Gosh, my job sounds so amazing doesn't it?)
I would recommend them to you but I do have experience welding and I would not recommend my style. Definitely go with leather boots, they don't tend to melt much from the occasional spark shower or dropped piece of hot metal. Also, I would recommend getting some Starter brand work socks. Black if you can. Grey tends to get stiff and rough over time, white is okay, but the black ones have stayed fluffy. they are a bit thicker than regular socks but make all the difference and offers some cushioning.