Bird Zero. The full build is great value for money on the components but it’s not cheap rubbish on there even with the basic spec.
You can go into somewhere like Evans and buy a cheap hard tail but the components are utter garbage and you’ll be replacing them within a month.
Frame build isn’t hard, though have to consider 26 or 650b if swapping stuff about. Though a “cheap” build can end up going a fair way over a grand anyway as I found when I built my c456. Started cheap with spare bits, probably knocking on £2k spent on it now 😀
Or… ride the Covert in the mud. Mountain bikes are actually designed to get dirty 😉 . Just having a pivot or two on it isn’t going to make it melt 😛
Though the real answer is buy a hard tail and ride both all year round.