Define "not too expensive", because there are some exceptionally cheap (both inexpensive and shoddy build quality) FRS/GMRS radios out there.
Straight FRS can be used without a license. GMRS requires a license, but one license will work for the whole family (or business, I think). GMRS licenses are about $80 and I think they're good for three or five years.
Straight FRS is limited to half a watt and has a two mile range at best, usually less (the antennae are not replaceable and are not particularly good radiators). GMRS radios can have much more power, and you can use, own, and operate repeaters (high powered radios that receive and retransmit signals to extend range to handheld and mobile radios).
For casual use, the FRS radios that come two-to-a-pack from Motorola, Uniden, Kenwood, Midland, or the other standard manufacturers are probably just fine, and will run you from $15-$75 for the set, with the price range varying features and quality.
If you know you need better range, get a GMRS set from any of thsoe standard manufacturers and get a license from the FCC and buy the radios. Count on higher power radios being a slight premium over the FRS radios, maybe $30-$100 a pair for the same features but higher power than the equivalent FRS models.
FRS and GMRS share some frequencies, but only GMRS licensees may transmit at higher power on those frequencies, and only GMRS licensees may transmit at all on the non-FRS frequencies. GMRS users may transmit on the FRS frequencies, but not vice versa.
Jim