Hey, sorry for the slow reply on live chat — we've answered you there now too.
It's not a bug, though I can see why it looks like one. Our extras — Dedicated Residential IP and Native Residential — require an active Standard VPN plan to run on. They aren't standalone products, so the checkout keeps the Standard plan in the order even if you try to remove it. We should make that clearer on the page rather than letting it look like a stuck toggle.
On what you're actually after: if you want proxy logins (host/port/user/pass, SOCKS5 or HTTP), that's Native Residential — billed per GB, from $0.70/GB. The Dedicated Residential IP is a fixed IP delivered as WireGuard/OpenVPN config files, not proxy credentials, so it's a different thing depending on your setup.
Cheapest way in is the 1-month Standard plan plus the extra you want. Happy to work out the exact cost if you tell us roughly how much traffic you'd use.