Yeah I was going to say, if you spend enough money you essentially guarantee that you won't be relegated.
I think there was a time when that was true, but a quick glance at the amounts that QPR, Norwich and Fulham have all spent in recent years illustrates that that is no longer the case. Most clubs in the topflight now have access to significant funds, either through a rich billionaire owner, the new TV deal or both.
What that generally means is that individual clubs aren't necessarily improving, it's just that more money is going to average players.
In the case of QPR, Norwich and Fulham, there were other factors that contributed to their relegation. As there were three worse teams/ squads than theirs in the seasons when they went down.