My only quibble is painting with the broad brush of "relief pitching"
Over half of the teams in MLB (18) spend less than $2M per RP, including closers with an MLB average of $1.8M. Only 4 teams spend more than $3M per RP. Teams average over $5M per closer (which is about 1/3 of the average bullpen spend of $15.4M)
Of the top half of spending on relief, 13 of those teams (MIN and MIL come in at 16 and 20, respectively) fall in the top half of payroll
Remove closers from the equation:
Only 4 Teams spend more than $2M per non-closer. Half of teams spend less than $1M per non-closer
I maintain that teams just do not spend big on non-closers