The Arsenal star is expected to join United this month in a deal worth a reported £350,000 per week. The Red Devils are also paying a transfer fee of £35m despite Sanchez being out of contract at the end of the season.
Such fees have a trickle down effect, claims Dyche, as clubs compare the value of their players to other deals completed around the league.
"It creates a tougher challenge because every time one of the super powers spends enormous money on a player that drip-feeds down the market," he said.
"So every player you then phone about has miraculously gone considerably up in value because they'll say 'well if he's worth that our players must be somewhere near as good as that'.
"So where does the next move from us come from? Where's the next valuation on one of our players or one of our targets?"