The Brookfield Board of Selectmen is proposing an $18.7 million budget for the coming fiscal year, while recommending a $43 million plan for the schools.  It's a 4.1 percent increase over the current year and would send the mill rate up by nearly 5.4 percent.  Town and school officials say they are taking into account rising special education costs, likely cuts in state aid and contractual salary and insurance cost increases.  $4.1 million for debt service, $1.3 million for capital projects financing and a $400,000 contingency are proposed.