Such decisions are based on available space and cash but more often on where the heart is. A G scale switching layout can be readily built on a 8 foot by 2 foot shelf by someone who is poor, and is an apartment dweller if the heart and mind are buried in and bound for this scale. When he is with his G scale shorty layout, he will enjoy it as much as a man with an empire, deep down. There is always a ton of issues to consider when choosing a scale, especially if you are crossing over to a new scale…Cost of the changover is just one. Beginners will tend to quickly find out if they chose the wrong scale for their situation, regardless of cost, in some cases.
The OP wanted to know if it was thought that there was a significant cost difference between scales. Even this is a loaded question? There is often found super high detailed work in a chosen scale as well as lesser quality within it. For some, acceptable quality within a scale is fine. Then, yes, there can be a tremendous differential. We need not think everyone here is a super high detailed modeler. Many just enjoy operating trains and to some of them, the acquistion of the best of the best within a scale is just a waste of their money.
Example… I can get the finest HOn3, metal, super detailed, K-27 mudhen with full sound from Blackstone at a train show for $340.00. The same level of quality and sound in an identical G scale K-27 will be at least $2,000.00! I consider that a rather healthy differential. You could pick and choose specific examples like this all day. Another guy can just as easily show where there is little significant differental. Too many variables for a definitve answer to the OPs question.
Richard