ACS comes in 2 licensing levels. Base and an optional "Large Deployment" add on license for more than 500 managed devices.
ISE is much much more than a TACACS+ server (in fact that capability was only added last fall with Version 1.4). However, to run it as just that, you need any number of ISE Base licenses (these are designed for client network access control use and serve to get any ISE deployment started) plus the Device Administration license. The ISE Device Admin license is not restricted as to how many devices you can manage. (Of course there are real world limitations if you have thousands of devices and something like a network orchestration /. automation system logging into each one multiple times per day, but for most customers this is not an issue.)
We generally don't use the support forums to discuss pricing as that's a more appropriate discussion to have with your selected reseller as there are things to take into consideration unique to your environment in order to build a proper bill of materials.
Generally speaking you would need either:
CSACS-5.8-VM-K9 (ACS 5.8 VMWare Software And Base License)
or
ISE-VM-K9= (Cisco Identity Services Engine Virtual Machine Image)
L-ISE-BSE-100= (Cisco Identity Services Engine 100 EndPoint Base License)
L-ISE-TACACS= (Cisco ISE Device Admin License)
...to get started.
The ISE bits add up to a bit less (about US$12k list price vs. about US$14k) as Cisco is trying to encourage customers to move to ISE unless they really really need some of the more unusual features that are only still available on ACS.
