That’s a good question! I haven’t been in this scene for a long long time now, so can’t say for sure.

I’ve been implementing an Instagram liker service back in... 2018 was it? So a stable pool of non-flagged residential proxies was important here, and it was my client who introduced me to the concept of “mobile proxies”. Basically, they use regular 3G/4G/5G modems with regular SIM cards, and expose that as a SOCKS proxy. You get a normal-looking IP from a pool of mobile operator’s IPs. Since mobile devices reconnect all the time (and are behind a CGNAT mostly nowadays), you can’t really flag an IP like that – and if it is flagged, you can get a fresh one in a moment.

I’m not using this mostly because I’m too lazy to research. Here’s a random one I found (so not an endorsement!) which is $1/GB, seems to only require email to sign up, and takes crypto (including XMR): https://floppydata.com/