£143 round trip from Budapest to London in August honestly doesn’t sound bad at all, especially with multiple big concerts happening at the same time.
With The Weeknd and Ariana Grande both in town, demand is going to be high. That’s the kind of situation where prices usually hold or creep up, not drop. The whole “book 1–2 months out” advice really only works when demand is normal.
If those dates are fixed around the concerts, I’d be very hesitant to wait hoping for a price drop. Saving a little isn’t worth the stress of prices jumping once more people lock in plans.
Personally, I’d book and stop checking. £143 feels reasonable given the timing.