ServerSupply.com is where we find a lot of older HP and Dell server and business workstation spare parts.
Just checked...they have a few there from no-battery cache models to ones with the batter cache. I recommend for your learning lab you do get one with the optional battery back cache...it allows higher RAID levels and doing online expansion, which, IMO, are important to learn.
Try to snag a bit more RAM.
As for hard drives, IMO, getting at least 4. Ideally you want a RAID 1 for the host OS...either Hyper-V or ESX and then the system drives of the guests, or a bare metal install. And create a larger second RAID volume, for the data of the bare metal install, or the data volumes of the virtual guests. For larger setups I usually setup that second RAID volume as RAID 10 for better performance.
Learning iLO of HP servers is good too.