Fair point, but take a look at the activity of the teams above us so far this January:
The current top two in our league have each only made one incoming signing - both loans.
Wycombe in third have made two signings, both loanees, although I suppose they're not really in the same bracket financially.
Cov haven't signed anyone, Pompey have made two loan signings and brought in a non league player for an undisclosed, but presumably small, fee, and Sunderland haven't spent money, bringing in loanees and Kyle Lafferty on a free. Peterborough have spent 500k on a non-league player, and it looks likely that the Maddison sale will go through to offset that, as well as two loan signings.
Of course, this could, and probably will, change in the next few days as the window wraps up, but my point is that no-one really seems to be bringing in established Championship-level players for a fee this window. A couple have invested in some non-league talent, but so have we. I'm not sure if this is usual of a promotion race or not, and perhaps its due to how tight the league is this year, with no clear candidates for a nailed-on promotion. But it doesnt seem like we're the only club having this problem.