Report generators for use with Drupal sites?

I need to recommend a report generator which will be used to produce management reports from my client's database. It happens that the web site is written in PHP but not in Drupal, although it's probably going to be converted to Drupal at some point.

I've found very little information about report generators' capabilities (apart from the publishers' claims), or unbiased reviews or comparisons.

So far I've found one possibly suitable product that's implemented in PHP: phpreports. Several others are implemented in Java: Windward Reports, Elixir Report, JReport, ReportMill, etc. And then there's Crystal Reports, which costs $$$$$$ but is powerful and widely used.

Has anyone had experience with these report generators, or others? If so, what would you recommend; what would you stay away from?

Here are some characteristics that it would be nice for a report generator to have, roughly in descending order of importance:

• It is moderately priced (a few hundred dollars at most) or free.
• It has a moderate learning curve; I can learn quickly how to create moderately complex reports.
• I can easily add code to provide functionality not supported by the generator, either by preprocessing the source data or by writing callback functions, or both.
• A non-technical user can easily learn to create simple reports without help.
• It can run on a shared server (it doesn't require any unusual extensions or changes to configuration files).
• It is implemented in PHP.

A client-server solution is fine if the client can run on MS Windows.

I've reviewed the Drupal modules currently available for report generation, but they appear to be limited to composing a report with a single SQL query. That probably wouldn't give me what I need, because some of the reports my client wants would be difficult to define by a single query, and if they were, they could not be formatted in a way that that users would consider accessible.