Range depends on many things.
1.Batteries. The new lithiumFePo4 are pretty safe and will give you more range at low weights and with less space needed compared to sealed Lead acid batteries(SLA) and/or other kinds of batteries. In lithium choose batteries with the highest Ampere-hour(AH) capacity per cell; and per pack(an arrangement of cells in series and paralel for an specific voltage and amp-hour capacity), for the size, weight and voltage you are looking for.
If recharging is an option at work, you might prefer those bateries and chargers that accomplish full charge in couple hours(2-5hours). Not all Lithium are the same. Some batteries are supplied with chargers and cell balancers that limit the charge to only slow charge(15 hours+).
2.Type of motor. A small motor with low amps needs, will take you further, but slower.
You will need to chose enough power for the hills around your area, since the stall currents are the highest. So the closer you are to the optimun RPMs the less amps will be needed. This is; Too little power available from an electric motor isn't good either if the conditions ask for a lot more from the motor.
3.Driving habits. The more agressive, the less range.
4.Wind resistance. The bicycles for the speed record on Human Powered Vehicles are recumbent bicycles inside an aerodynamic shell. A human can only pedal at 3/4hp max. With this low hp, those HPVs achieve speeds above 80mph!!! or in the case of range, I believe well above 35miles if electric assistance is used. An aerodynamic shell would help, or at least a bubble shaped windshield.
5.Road tires instead of mountain bike tires; and inflated at the correct psi.