Depends what you mean by cheapie. Looking at 450-600 players, the forwards with a shot of becoming 750k players due to age/improvement/ability are EKatoa, Tino, Rudolf, Radley Tupounuia. Barely been discussed other than Tino and he's the only one in any of my squads because of other, cheaper options with more cash-generating certainty in the forwards but I'd expect at least one of the others to turn gun this year.
Backs have been fully discussed. TTrbo, Holmes etc in the WFBs. Debates over Brooks, Morgan, CHT, Lam, Milf in the HLFs.
Not sure about the criteria for your original list. Best and Grant weren't mid-rangers last year. Neither, at the other end, was Harris.
Have adjusted my original post, categorising players that took the leap to gun keeper. Harris started last season priced with a BE of 47, and finished with an average of 60, moving him from below gun keeper to top tier forward.