Recently, renewable energy (RE) has been introduced as a promising solution to reduce the "non-green" energy consumption of cellular networks. In this paper, we study the electric bill reduction of a cellular network powered by both RE sources and the power grid in a variable electricity price environment. We decompose the problem of electric bill reduction into three sub-problems: RE allocation, energy consumption minimization and radio resource allocation (RRA). In this context, we propose a new algorithm that adjusts the network configuration to increase the utilization of RE. Results show the efficiency of our proposed algorithm, where it achieves 30 % reduction of energy consumption and outperforms a benchmark algorithm with a gain of up to 20 percentage points in terms of electric bill reduction.