Can be done cheaper, sometimes it's just a matter of being in the right place at the right time. Trawl fleabay on a regular basis for Ka lnb's and one day you could get lucky. The little white coloured Band A-18GHz 'Hughes@ DRO lnb's don't need any mods but you do need the correct WR42 scalar feed to suit which type of dish you will be using it on ie: PF or Offset.
For an alternative to the now unobtainable Inverto Ka/Ku lnbf (Band D on Ka) Iv'e followed s-band's, Grahams lead on modding ex-satellite broadband Gilat ODU's by removing the Rx board, grafting on a suitable WR42 feed, re-house & waterproof it and away you go. The one that i have modded for use on 16/7/4.9° East satellites actually performs better than my Inverto Ka/Ku but are Ka only and one polarity only - which ain't to much of a problem at the moment as all the broadcast Tv action is on Hor polarity. Again, these can be picked up off the bay from anywhere between £20 to £50 - depends how lucky you get .