BPM Standard -
The core of BPM Standard is the software that was acquired by IBM when they purchased a company called "Lombardi Software". The product was known as "Teamworks" and that is why, for example, the variable namespace in IBM BPM starts with "tw." Standard is best used for Process Solutions that have multiple Human to Human and Human to System handoffs to accomplish a business goal. Because of the interpreted nature of code written in IBM BPM standard it is not recommended (in general) for solutions with high data through put or data manipulation requirements. If you need to process millions of process instances per hour (which implies little human interaction) BPM standard is not the right tool.
BPM Standard has (today) significantly better tools for generating UI for a process quickly and iteratively without requiring a deep understanding of the J2EE stack.
Standard models process using Business Process Modeling Notation (BPMN)
BPM Advanced is the Heritage IBM solution in the BPM space. It is "closer to the metal" in that the code written for Advanced follows a much more traditional SDLC. The actual assets are deployed as ear/war files to a WebSphere server. Advanced has support for more sophisticated transaction (e.g. 2 phase commit) and comes with some very nice tools for easily doing data transformation. It is much better suited to "lights out" processes that need high throughput with little human interaction.
BPM Advanced is not typically used to create UI into processes.
BPM Advanced models processes using Business Process Execution Language (BPEL).
I don't know the current pricing, but IBM BPM pricing is based off of "PVUs" which I believe is an IBM specific unit of measure (see https://www-01.ibm.com/software/passportadvantage/pvu_licensing_for_customers.html
). Since you get "Standard" when you buy "Advanced" it would be safe to assume that Advanced costs more per PVU than Standard. I don't think I've seen anyone buy fewer than 140 PVUs for a given environment, and generally you need 3 environments (Dev - Test - Prod) minimum for a BPM solution.
If cost is your primary concern you might look at BPM on Cloud (BPMoC). This gives you access to a full BPM Standard environment with pricing being (I believe) per user instead of hardware based.