I've this week setup a Gigaset N300 IP system. Works nicely and very impressed with it. Not expensive for what it does.
I've also run Voip through a number of Draytek V model routers in recent years, and that works well. Sometimes took a bit of work to get the configs right.
Also I ran a number of Linksys ATA units, like the PAP2 series, for a few years. Again those worked well. Although getting the configs right took a lot of time, especially at first. Yes those were cheap.