Dyche at Burnley said such deals as van Dijk means it is a major challenge to keep up.
"Nothing is impossible in football but sometimes probability outweighs possibility," he said.
"The way it is going it is harder and harder. We saw with Leicester it is not impossible, but it is improbable.
"If you have a team like Manchester City spending £100m on three full-backs that is an interesting thing. With Liverpool you have someone spending £75m on a centre-back and there are not many clubs who can compete with that.
"That £75m is probably pushing our transfer budget forever, or very close.
"That's one player against the history of another club - in the same division. So that's going to be hard to narrow the gaps on."