Most of the commonly-available low-power short-range RFID kit works on either LF (Low Frequencies - of the order of 120-150 kHz) or HF (High Frequencies- in this case around 13.5MHz). Although terrestrial radio propagation is generally further at those lower frequencies, the permitted radiated power is so low that the effective range can be of the order of just tens of millimetres at LF (as used to 'chip' your pet) or a little more in HF kit.
Longer range RFID kit typically operates at UHF (Ultra High Frequency) - typically in bands around 430MHz, 860MHz and 910MHz depending on your local legislation. Unfortunately the much smaller market for UHF RFID typically adds an extra 0 or 00 to the end of the price tag.
Try googling for RFID UHF and that may help narrow your search.
Dave