Transfer fees don't really mean a whole lot below the top few clubs - the main correlation is between wage bill and league position. From memory, Everton were the 7th highest spenders on wages for most of Moyes rein, though I would need to look up the exact stats.
For me Moyes did a good, if unspectacular, job at Everton. He was good enough not to be sacked despite plateauing for about the last 6 years, but not good enough for a top club to take a chance on him. Ask yourself this, if Fergie had spent over a decade managing Everton, what would he have achieved (bearing in mind he broke the dominance of the Old Firm in Scotland with Aberdeen on a shoestring and even beat Real Madrid to win a European Trophy)? That's the kind of managerial performance at a smaller club which makes it worth taking a chance on them.