CCS process for a drink dispenser with two different prices
You can easily profit from warfare that way:

$$ M \stackrel{\mathrm{def}} =
  c.(
    d_{\text{tea}}.\bar e_{\text{tea}}.M
    + r.\bar b.M
    + c.(
      d_{\text{coffee}}.\bar e_{\text{coffee}}.M
      + r.\bar b.\bar b.M
    )
  )
$$

note that you have to press refund to get a tea if you put too many coins. If you don't want that, you can adapt it (or maybe set up a (finite is enough) counter) :

$$ M \stackrel{\mathrm{def}} =
  c.(
    d_{\text{tea}}.\bar e_{\text{tea}}.M
    + r.\bar b.M
    + c.(
      d_{\text{coffee}}.\bar e_{\text{coffee}}.M
      + d_{\text{tea}}.\bar b.\bar e_{\text{tea}}.M
      + r.\bar b.\bar b.M
    )
  )
$$