Section 30. At the request of any department, and with the approval of the mayor and city council under Plan A, B, C or F, or with the approval of the city manager and the city council under Plan D or E, the city council may, in the name of the city, purchase, or take by eminent domain, under chapter seventy-nine, any land within its limits for any municipal purpose, and, without the request of any department, but with like approval, the city council may, in the name of the city, purchase or take by eminent domain, under chapter seventy-nine, any land within its limits for the purpose of conveying the same, with or without consideration, to the commonwealth for the use of a regional community college. Whenever the price proposed to be paid for land for any municipal purpose is more than twenty-five per cent higher than its average assessed valuation during the previous three years the land shall not be purchased, but shall be taken as aforesaid. No land shall be taken or purchased until an appropriation by loan or otherwise for the general purpose for which land is needed has been made by the city council, by a two thirds vote of all its members; nor shall a price be paid in excess of the appropriation, unless a larger sum is awarded by a court of competent jurisdiction. All proceedings in the taking of land shall be under the advice of the law department, and a record thereof shall be kept by said department.