Depending how many people you work with it could cost a fair bit.
I'd be cheap and bake a dose of mini cakes.
(
Maffers I flow kinda strange like Spina Bifida footprints, Sun 17 May 2009, 14:09,
archived)
I'd be even cheaper and just not buy any cakes.
It's my birthday, after all.
(
WHARRGARBL, Sun 17 May 2009, 14:10,
archived)