If youve only got $20 to spend its probably best spent on a SL1PLL, if you can afford $60 an Invacom QPH-031 will probably perform just as good or better. Ive had one for years and its held up very well, plus dual circular / linear is really nice. Freq stability is important to a point, if you can maintain 1mhz stability your good to go in most cases, modern tuner/demods will have no problem accounting for 1mhz drift or more even. Any decent lnb will do 1mhz or better stability. noise is more important now days. A quality DRO will always beat a PLL for noise.
When your in $20 price range there is ALOT of junk in that range, the SL1PLL is an excellent $20 lnb, its not $150 norsat but its an excellent lnb for what your paying for.
UDL