There is no easy answer to this; it is difficult to deliver reliable comms over 5 miles in mountainous country. The solution usually used by RAYNET and the Royal Signals is to put an unmanned repeater station somewhere high up and configure the hand held radios to relay through it. This is not really a long term solution though (mind you, Canadian radio amateurs install solar and wind power and just leave the weatherproofed repeater up the hill. Works for them.). An alternative is to use a technique called NVIS which will give reliable comms in this situation, but requires horizontal wire antennas several metres long.
Options include:
PMR 446 radios. Dirt cheap, UHF, licence free, but only half a watt to an integral antenna. Realistic range a mile at most (but >20 miles hilltop to hilltop). You will not be able to talk from valley to valley, as it is approximately line of sight.
Private business radio. VHF at 5 watts or UHF at 4 watts. Base or mobile stations can have more power. Licence needed, but thsis just needs money and no qualifications. 2 to 10 times the cost of PMR 466, but range slightly better, and equipment more robust.
CB. Up to 4 watts out. You might get 1 to 3 miles on ground wave even in the mountains. Hand helds available and cheap. Two sets of HF frequencies around 27MHz, UK only and European. UK freqs might be withdrawn in 2010 (no decision yet). As wavelength around 11 metres, really needs a long (2.5m) antenna to be useful, and 'rubber duck' aerials will be inefficient. You will get a lot of interference ('skip') in sunspot maximum years.
Amateur Radio. Three levels of licence. exam needed, plus 15 pounds a year. Can use up to 400watts on highest class. No commercial use allowed. All operators must be licensed and use government allocated callsigns. VHF and UHF handhelds -same pros and cons as private business radio. Satellite use possible but not helpful in this scenario. Some amateur repeaters are well sited and you might be in an area with good coverage.
