I'm working on a project right now building a data warehouse against JDE/AS400 (and lots of other data sources). You have two components - the ETL/data warehouse and the mining tools/front end. I'm guessing you are really asking about reporting/ad-hoc queries, not data mining. There is a big difference.
If you want reporting only I think these tools you mention would work - provided they know how to deal with JDE decimal points and date formats. Most generic products will require some work to handle these quirky JDE datatypes. I just posted a question on this forum on that subject.
The cheapest is to use Excel with As400 as the data source. You can create views of the F4211,F0101, etc with cleansed dates and decimals. With Pivot tables the users can create queries (limited to 65535 records). Warning - your AS400 may be severely impacted by large queries.
Keeping in mind that Oracle intends to tombstone the JDE product by 2013 you may want to invest in a product that works against an Oracle database in the future.
