Amateur radio is the way to go. Some details...

You will have to pass a written test to get your technician license. The fee for the test is under $20, and expect to spend around $20 or so for a study book (you and your wife can share).

About the equipment. A technician license will allow you to use 50MHz and up. 2M (two meters) is your best choice. Get a mobile radio. These mount in your car, and will transmit at around 50 to 60 Watts or so (depends on model). With two of these, you should be able to talk to each other from 20 miles or so (very rough ball-park figure). Of course, this depends on your terrain. Going from mountain-top to mountain--top, you may get 50 miles. From one valley to another, you may get 5 miles. It all depends on where you live.

This assumes that you are talking directly to your wife. This has the advantage of not needing anything else. But you can extend your range a LOT using a repeater. Instead of transmitting to your wife, you would transmit to the repeater, which "repeats" the signal at a higher power. Repeaters usually also have a better antenna, which is mounted on a high tower for better reception. It is not that uncommon to be 60 miles and be able to use a repeater. The only problem is that in an emergency, you might not be able to depend on the repeater. They can loose power (but many have emergency power), or they can be damaged by whatever the problem is (especially weather).

Also, keep in mind that HTs (walkie-talkies) have VERY limited power and rather poor antennas. You can easily work a repeater with one from twenty miles away (depending upon terrain), but going from HT to HT, you will get about the sam range as a good GMRS radio. I would expect five miles at the most. I have had problems talking from one end Disney MGM Studios to the other end using a 5W HT.

If you want to spend a lot of money, you can make HTs more usable. You can get a dual-band mobile unit with cross-band repeat. Your HT can talk on the 440MHz band, which talks to your mobile unit. Your mobile can act as a repeater, and transmit on the 2M band at the full 50 watts. This means that you can have the full 2M range, but you are still limited to being a couple of miles from your car. This will also kill you battery unless you rig up a 2nd battery just fro the radio.

*** EDIT ***
There are several models of 2M mobile radios available in the $160 to $180 range. Expect to spend around $50 or so for an antenna. Throw in some misc. hardware, wire, and cable. So it would take around $250 or so per vehicle, plus a few hours of sweat. You will also need to electrical tools for the installation. A VHF SWR meter is around $35, and a basic multimeter can be had for $20. A soldering iron for $10 may help, too. This assumes that you have access to the usual drill, pliers, screwdrivers, etc. You could likely find a couple of people eager to help give advice on the installation at your local amateur radio club.