Unless budget is a huge consideration, then I'd say go both CB and FRS.
Should be able to find a working FRS handheld or two, at a flea market for $5-20 I would say. Just make sure it has tone capability (CTCSS encode at least). Get one that takes AA batteries and invest in at least one set of batteries to use and one backup set, preferably Eneloops. AAA batteries have less capacity and will drain faster, and proprietary battery packs (we are talking for type-accepted "bubble pack" FRS, not Baofeng and the like) tend to be junk.
For a CB, better to spend $5 on a yard sale/flea market radio and $50 on an antenna, than $50 on a radio and then use a junk antenna. Performance (and thus your satisfaction) is all about the antenna. [Note: In case you're wondering, detachable antennae have been prohibited on type-accepted FRS for years, which is why I didn't mention this above.] At any frequencies, the longer the antenna, the better, however it's not always practical. With CB having such a long wavelength, if you think about an antenna for a higher frequency whose length may easily fit on your vehicle, that same length becomes a source of major signal loss if you use a short antenna for CB. You don't see 1/4 wave whips on vehicles just to look cool, rather they are for optimum performance. It's hard to word this in non-technical terms, but my point is that on CB frequencies, don't think you are going to get away with a simple and short little antenna like you may see on your local police cruisers, rather you are going to need something of much more length. Of course, none of this matters if you only need to talk for a few hundred feet or a 1/4 mile or something, in which case a tiny CB antenna will work just fine.
