You should get LNB's with a local oscillator stability no higher then +/- 500kHz
I use Norsat LNB's a 8115 for C-band 17K +/- 100 khz L.O. stability and for KU I use a 4207a wich is a .7db +/- 250 khz stability the C-band was about $130 and the KU band was $108. I have tried using cheaper LNB's but I had trouble with them and they did not last very long before they started drifting bad and would cause stuttering on some signals. Analog was more forgiving of cheap LNB's
