Hi Katarina,
You could setup an automated rule to send you an email when the account reaches a certain amount spend in each month. but that would leave you to pause the campaigns manually. Or you could implement a script to automatically pause the campaigns when a specific amount spend in the account is reached and to restart at the beginning of the month. PPC Hero has more information on this here http://www.ppchero.com/advanced-adwords-budget-script/
Hope this helps