From a certification testing point of view, I'm not aware of huge savings, but also can't claim much relevant experience. That will change soon as SIL testing is to be a big part of my next few years.
However, from a research or developmental testing point of view, huge savings can be realized. The cost of developing the SIL will be the greatest factor, but if planned properly that cost could be distributed over many projects. Many of the benefits come from the ability to rapidly test and amend software loads, sometimes even during a test sortie.
For example, our CDU software was developed over time through flight test and operational experience. 15 years later version 9.1 comes out and few are complaining about the software, other than desiring future development. The HUD symbology, however, was developed on a low-fidelity simulator by having 20+ operators with various backgrounds try it, propose changes, then try the changes. Version 1 is still in use 10 years later.
When you crunch the numbers, ensure you compare the cost to get identically matured product.
Cheers,
Matthew.