The best on-site backup is a Synology NAS.
As of Feb 2023, here is a good system
3 10TB drives @ $250 = $750
could add additional memory or SSD cache but typically isn't helpful for backup
Total: $1350
Synology comes out with new versions every year. The last 2 digits of the versions is the year it was released so the 923 was released in 2023.
You could save money by getting a cheaper Synology like the DS220+ which is $300. If you got the DS220+ then you would only have to buy 2 drives since it only holds 2 drives. So that total cost would be $300+2*@250=$800.
All but the cheast Synology NAS comes bundled with the Active Backup for Business program which works really well. Don't be like me and accidentally order a Synology NAS and not check to see if it supports Active Backup - never making that mistake again!