The Methacton School Board next Tuesday will consider a preliminary budget for the 2012 - 2013 school year.   The proposed spending plan totals about $94,400,00 at this point and district officials are leaving the door open to request approval from Harrisburg to raise property taxes above the index established by state law.   District officials say if the exception for their contribution into the state retirement system sticks, the increase could come in at just under 3%.   That translates into about $140 for the average homeowner.