Personally, I don't think you need to invest a lot of money to do well at Championship level. Look at Sheffield United and Bristol City; they haven't spent much on their squads at all, and yet are both currently occupying the play-off positions. Cardiff's squad last year was far from being the second-best in the division (contentiously, none of their players made it into the 'Team of the Season' for that campaign), and yet they won automatic promotion. The year beforehand, Huddersfield were tipped for relegation based on their squad, but through acquiring successful loans and a shrewd boss in Wagner, they also managed to win promotion.
On the contrary, Nottingham Forest, who spent around 60 million in the summer, have had to settle for mid-table mediocrity this season. Stoke have one of the best and most valuable squads in the league on paper, with a PL quality goalkeeper in Butland, and players that are probably on very high wages, yet they are occupying the lower end of mid-table.
I think that, although substantial spending does help, you can do quite well in this league simply by having an astute manager e.g. Wilder, Johnstone, Warnock, Wagner, etc, who knows how to get the best out of a more limited set of players, as well as having a good recruitment team.