I too like to have a selection of half bottles. I don't have that many, but they are useful to have around.
If you're looking to pick some up, wine-searcher pro allows you to specify bottle sizes as part of your search criteria. Fine & Rare - who I know you are familiar with - have F07 @ £22.45, F03 @ £19.50, Silval 00 @ £17, Ni97 @ £22 (interesting!...might not suffer the cork problems), GC80 @ £21. You can also often come across Warre and Dow 1983 and 1985 in half bottles on the auction market for the sort of price that you have in mind.