If you want to enjoy the full benefit of GMRS avoid all of the cheap radios being promoted on these pages and search and read carefully the threads warning or discussing "Cheap Chinese Radios" and "CCR". The market is flooded with such products and they are JUNK. Even some of the Motorola GMRS radios are awful as they are just toys.
You will be spending a lot of time listening and talking on your radio and need to enjoy the full benefit of the service.
I would look for a commercial grade radio, even one in good condition that has been pulled out of service as opposed to the Midland GMRS radio. There are dealers on e-bay who will provide such a radio and program it for you. You can spend $100 or $500 and you will be happy if you do your research carefully.
Personally, I think a 45 or 50W mobile (dash mounted) with the FRS main channels programmed in both SIMPLEX and REPEATER mode with the 141.3 Hz CTCSS travel tone would be a good start. This would occupy 16 channels. You can buy radios with 128, 256 and 512 channel capability which means you can load up repeaters from MyGMRS along your routes with specific CTCSS (aka PL) tones. I would also load up a zone (group of channels) with simplex, the travel tone on TX and carrier squelch only and set this up as a scan group so you can listen for activity as you travel. Note you will hear people that may have their radios set to a different CTCSS code, so they may not hear you.
You can program multiple PL select in some radios to enhance the utility. But this gets very fiddly if you are driving.
The interstitial channels, the ones ending in xxx.xx25 can be programmed as well, however read carefully the FCC rules on power level because you will be limited to about 5 watts. If the radio can have power set on a channel by channel basis to low power, you should be OK. Having the interstitial channels will permit you to talk to FRS radios.
The GMRS service will permit up to 50 watts power to the antenna and +/- 5 KHz deviation. If you shop for a radio it will have an FCC ID number which you can search using Google and a widget will find the FCC filing or you can go directly to the FCC OET site and search there, though their site is hard to use.
What you will find is the FCC "Grant". My notes in (brackets)
(EXAMPLE
KENWOOD TK-805D K1
https://fccid.io/ALHTK-805D-1
FCC IDENTIFIER: ALHTK-805D-1
Name of Grantee: Kenwood USA Corporation
Equipment Class: Licensed Non-Broadcast Station Transmitter
Notes:
Modular Type: Does not apply
Grant Notes:BF
FCC Rule Parts: 22, 74, 90, 95
(You want a Part 95 radio, but nobody will know the difference if you use a Part 90 radio that otherwise meets the FCC rules.)
Frequency Range (MHZ)450.0 - 475.0
(This covers GMRS 462/467 MHz nicely)
Output Watts:25.0
(You can operate up to 50.0 watts at the transmitter antenna terminal)
Frequency Tolerance:0.0005 %
(This is equivalent to 5 parts per million GMRS requirement)
Emission Designator: 16K0F3E
(GMRS Emissions are 20 KHz Bandwidth on the 8 main channel pairs 25 KHz spacing, 16K0F3E translates to +/- 5 KHz deviation and 3 KHz voice bandwidth or ( (2 x 5Khz) + (2 x 3 KHz) = 16 KHz ), In some cases you will find radios advertised for 20K0F3E and that is fine. What you don't want is a radio that does only 11K3F3E or some lower value like the Midland GMRS radios are locked to.)
BF: The output power is continuously variable from the value listed in this entry to 20%-25% of the value listed.
(This is a typical notation, read these as sometimes there are qualifications that one should be wary of)
I hope this helps you..