Luis H. if accuracy is the priority, can check betterenrich.com it pulls from 17+ data sources and provides only direct mobile numbers (no landlines, voip or toll-free etc) using a multi-layer verification system.
Luis H. Cheapest way is: run your list through a phone enrichment API (like Apollo, Kaspr, Lusha, etc.) and set it up in Clay so you only pay per successful number found instead of bulk credits. That way you keep costs super low