Dataspeed relates to bandwidth by Shannon's theorem which states that the maximum capacity (C) that can ever be sent over a digital channel is set by: C = bandwidth * log2(1+S/N), where S/N is the signal to noise ratio. That is, double the bandwidth, double the maximum theoretical speed. So, to steal an example from Wikipedia: if the signal to noise ratio is 20 dB and we have 500 Mhz of bandwidth we can transmit at 3 Gbit/s (theoretically at least).
Also important to understand is that the lower the transmitting frequency, the further the signal will go (given the same transmitter strength). Going from 1 Ghz to 500 Mhz and you double the transmission range without increasing the transmitter strength.
To make this equation even more difficult, the lower the transmitting frequency, the higher noise level. So in conclusion this means that more bandwidth gives us higher transmission speeds and higher frequnecy gets more expensive since we need more transmitting towers but has low noise levels and therefore acheives higher speeds.
Hope this explains things!