Dvr recommendations ?

My buddy bought a new place that has 7 lorex cameras but no dvr. He asked if I could help him out. The only problem is that I haven't touched this stuff in ages. Its been all IP based and systems with 100 to 1000 cameras. So what is the current recommendation decently priced to cheap option. That can reuse what he has and leave open to adding some new ip bases stuff in the future.