I did BCMSN with a single 2950 SI and a 2911XM with a couple of fast ethernet ports.
The amount of L3 stuff in the BCMSN is minimal. There is a bit of configuration, but with the EI image you should be able to do 80% of the lab work. Unless you are heading for CCIE where you need really an L3 switch or two of your own, I'd save the cash on a third switch, and use it on the off-chance that you don't pass the exam first time. You honestly won't touch it again until CCIE.
Your money, tho... your call.