The Saudis have had assisted recovery at Ghawar since the 70s.
Even now, it is far lower costs than here in US
Their average costs are significant lower. But their marginal cost, the cost to produce the next additional barrel is getting expensive, relative to their past production costs.
Have you looked at what they had to do for Manifa?
CGES: Manifa Is an Expensive Development
http://www.rigzone.com/news/oil_gas/a/127903/CGES_Manifa_Is_an_Expensive_Development
The CGES revealed that estimates of investment intensity per peak daily barrel range from the ultra-cheap $2,500 (per peak daily barrel) for development of the Haradh III zone of the supergiant Ghawar oilfield to $10,000 for the massive Khurais et al development and finally $17,500 for the Manifa field, the most expensive development in Saudi Arabia.
They are not spending those dollars because they have a surplus of cheap oil sources.