Is there a way to grant access to a folder in standard reports to a user . We have about fify application areas that have different users. Our original idea was to create a domain for production, test and development. Do we have to create fifty domains to solve this ?

If you're just using MRE, then yes, you would need separate Domains. Once a user has access to a domain, they can see everything in that domain. There are workarounds if you're using Dashboard. You can use Role Tree which gives users access to specific reports. Or, you can remove the "tree" link and only give users access to reports through folder or link blocks.