When I started to buy CDs in 1986, the standard price for a full price disc was £11.99. As different price ranges were introduced, a mid-price disc was £7.99, a budget price disc £5.99 and a super-budget disc (Naxos) £3.99. The VAT increase of 1991 saw some odd pricing until everything got rounded up to the nearest 50p. Naxos went rapidly to £4.49 and then £4.99.
I did find it very annoying that multi-disc CD sets were always priced at single disc price times the number of discs. This didn’t apply to vinyl, e.g £5.99 for ‘In Rock’ but something like £7.99 for ‘Made In Jaoan’.