Do not buy techs ahead of thier times and you'll never worry about MP cost for buildings.
They SHOULD cost MP, and as someone stated, they should cost more!
10 temples = 10 basetax for 100 ADM. Try coring a 10bt province for that cheap.
Some of you seem to think buildings are weak, I can tell you they are not... Buildings are powerful and worth every MP they cost. Dont forget that most buildings provide more than one benfit. Temples add cash, of course, as well as forcelimits. Workshops increase production income as well as trade income. etc....
Provinces give more than one benefit too.
Land > Tech > Ideas > Buildings...most of the time, with some exceptions. But, buildings are not as far behind as people often seem to suggest, and are less expensive in different resources than other investments in some cases.