While £5.6m would have got you a lot more, you're well over estimating what it would have provided in quality. Moyes often operated on a shoe-string budget.
For reference, Beattie was £6.5m in January 2005, Phil Neville was £3.5m the summer after and Yakubu was £11m in 2007. So, £5.6m was not a huge sum.
When you consider that his net spend was so little, I think it's fair to say he did really well with his acquisitions and no wonder we had to slowly build.
As I've previously mentioned, a bit of Moyes's shrewdness and diligence wouldn't have gone amiss during the early year's of Moshiri's tenure as owner.