Cheap and not flagged as VPN rarely go together with ISP. The ones that show up as VPN are usually datacenter ranges sold as ISP, the ASN gives it away. Before buying in bulk, take 2 or 3 test IPs and run them through ipinfo or scamalytics, if the ASN is a hosting company instead of an actual ISP like Comcast or Verizon, skip it. Speed wise real ISP should be fast, if it's slow the IPs are probably shared with too many people. Disclosure, we're DataImpulse, we don't sell ISP, but if the static IP isn't critical for you, sticky residential sessions rarely get flagged as VPN. For logins or checkout you usually need the same IP for one session anyway, not for weeks. What are you using them for?