The Bill Nick way but on a little diet.
Sign one decent player every year around the 40m mark that should improve the first team.
Get rid of dead wood , move on players that can be upgraded .
Sign one long term cheap prospect around 10 to 15 every 2 years and introduce academy players if they are good enough.
Around a net spend of 30 to 40m each year.
With the money awash in football , this would be possible even including the stadium build but sadly another round of infrastructure projects will dent this .