I got this big bag of BB5 pads last year for my CX bike:
https://www.amazon.co.uk/dp/B09N1NKLFF?ref=cm_sw_r_apan_dp_VNDRKWBR36YBS38REHE7_1&ref_=cm_sw_r_apan_dp_VNDRKWBR36YBS38REHE7_1&social_share=cm_sw_r_apan_dp_VNDRKWBR36YBS38REHE7_1&starsLeft=1&skipTwisterOG=1
7 pairs of basic resin pads for a fiver.
Admittedly my expectations were low and I thought I’d be changing them every other race (on a bike basically intended to be ridden in one hour stints) but they’ve lasted better than expected, still on the first pair after more mixed mileage than I originally intended, and they do work at least as well as any other pads I’ve used with the BB5s (better than some TBF).
As ever with mechanical discs, best investment is in decent outers and cables, if they’re a bit mushy knackered cables are often worth checking for.