The South Africa international departed Goodison Park to join Spurs for £3m in January 2011, but he returned on loan during the second half of last season before making his Toffees return permanent in a £4.5m deal.
"I was delighted to get Steven back, although financially it wasn't so good for us," Moyes explained.
"We tend to do good deals at Everton but we had to buy Steven back for more than we sold him and he was a year older.
"We knew when last season finished that we had to bring Steven Pienaar back to Everton, really at any cost."
Pienaar, who is also receiving a significantly higher weekly wage than he was prior to his move to Spurs, is expected to feature in his side's Premier League opener against Manchester United on Monday night.