I had good luck getting new bumper plates from https://giantlifting.com/. Their prices might look a little higher compared to other sites but shipping is free to most states and they're pretty transparent about their rates. 360 bucks for four 45 bumpers shipped from WA to PA.
P.S. Are you making any of the code open source? It might be cool if enough of the scraper is transparent so that other people could contribute new sites. I made something similar a while back for people to find the cheapest sale prices on groceries and the biggest headache was adding handlers for the additional sites.