Brushless are technically more efficient than brushed motors, but because of their higher output and requirement for a more complex ESC, you might notice slightly battery life - it really depends on the motor and ESC you're using... I guess it boils down to what you're going for, longer battery life or higher performance.
If you just want the battery to last longer, then there's not much point forking out the money for li-ion; just get a higher capacity ni-cad and a fast charger.
If you want performance, you'll need to go brushless. My advice would be to go brushless then upgrade the batteries when time and money allow. I can't say what the quality of that motor/ESC is, but the motor is the cheap part so don't worry too much about it going pear shaped