Why DONT you want to build a DW? apart from a pretty steep learning curve, I don't think there is any licencing issue with R2
you can build pivots for specific datasets, or you may be better off connecting XL to the R2 database and using pivot tables
A lot of cube type analysis can be done in SSRS as well.
How big is your data, how GOOD is your data and how well indexed are your tables. On the primary tables, are you mainly inserting records or are there a lot of updates and deletes as well. Is the database OLTP (transactional) or OLAP (analysis and reporting)
Do users need to be able to summarise and drill down in many different ways, or do they just want pretty reports. If the latter, then SSAS may be overkill, you can do the same using nise SSRS reports.