Upgrading from CF 9 to 2016

I can't answer your price question. Code wise, for us, upgrading from CF9 to CF-2016 was fairly painless. Only four issues come to mind that affected us:

1. CGI.PATH_INFO is not set and we needed to add code to use CGI.SCRIPT_NAME if the former was empty (I could be flipping these, I'm writing from memory).
2. File tags are slash and backslash sensitive whereas CF9 didn't seem to care - C:/temp/filename.txt and C:/temp\filename.txt were perfectly valid in CF9 whereas only backslashes are valid in CF-2016 (on Windows).
3. Passing REQUESTTIMEOUT as a URL parameter no longer works. Your lengthy pages (if any) need to use the cfsetting tag to specify the timeout.
4. We use an /API folder in our apps and CF by default treats this folder as a reserved folder for it. This was probably the most painful for us but we figured out the right tweaks to "unreserve" the folder.

I will say though that the improvements to the cfscript language, capabilities, and syntax, along with the addition of queryExecute and related tags vs. the query.cfc component makes it well worth any upgrade pains you might have.

There will be potentially a lot to consider but it depends on the complexity of the code. You can get the trial of 2016 and run the code analysis in the CF Admin. Although not perfect, it will give you a start on what might have been depreciated.

The only real way will be to migrate in development and test it fully in the newer version.

There isn't an upgrade path either for 9 to 2016 I don't think - You just have to buy the license for 2016 and install it separately. It uses Tomcat now instead of JRun so a lot in the underlying engine is different