At least double. When you do two things instead of one thing and both of those things are similar. Calling a method to access a field ALSO requires looking up a field. So at least double.
But if we break it down, from an access perspective a field access is going to be faster than a method access. Method lookups require a more expensive lookup because the method could be defined on different classes... it's a polymorphic lookup. Fields cannot be overridden and so the proper class was resolved at compile time.
But even aside from the lookups. In one case, you have a byte code to retrieve a field. In the other case, you have a byte code to invoke a method that will then have a byte code to retrieve a field. Having been in the JVM code many times, I cannot possibly imagine how a field access would be SLOWER than a method access.
Therefore, logically, the method is at best the same timing as a field access... ie: method + field access is at best double field access alone.
All together it's probably at least 3 or 4 times... but double is safe to say.