For me, it's way too much. In silver, you don't need legendary and you don't even need card above LVL1.

I'm in 1800+ SILVER and i spend less than 22 DEC a day to sit at SILVER III. If i want to be in SILVER I, i will probably rent just for power and it will cost ~150 DEC in total.

A lot of usefull card cost less than 1 DEC/DAY (Creeping ooze, Goblin mech, Nectar queen, Sea monster, Sand worm, Venari Wavesmith, Djinn Renova, ...). You can rent for less than 10 DEC/Day of useful cards and the rest in power.

For power, check peakmonsters and try to rent card over 500CP/DEC.