I live in a 110 foot hole. I gave some thought to this very issue. If you're going to spend any money, just do it properly, such as using the equipment mentioned above. Otherwise you're going to spend a bunch of extra money and time trying to get the performance you want.
I have a 2m repeater and a 70cm repeater at my house. I would put up a GMRS repeater if I thought my wife wouldn't toss me out...
There are several ways of doing this and each has its advantages and drawbacks.
Personally I use a portable duplex (two frequency) repeater. This does require a tuned duplexer. The duplexer I have is commonly refereed to as a "Flatpack" duplexer. It does need to be tuned which most local radio shops do for $50-$100. Because of the nature of flatpack duplexers (Being cheap and not as good as BPBR duplexers) once they are tuned you should be able to use any of the 8 repeater channel pairs without needing to be retuned. The flatpack I use is a Celwave UHF duplexer, and I can run from .550-7250 with no issue. The drawback of this system is power output. The more TX power I put into the duplexer the less efficient it'll work causing de-sense of the signal into the RX radio. While the repeater will run 25W, I find I usually run it on low power using 10W of power instead. This system is also likely most expensive as it requires more equipment to operate. Still, my repeater build came to about $250 not including the antenna, feedline, or power source.
Simplex repeaters are the cheapest option as they use the least amount of equipment or parts or even run off existing installed radio hardware. The unit does not require a duplexer or second radio to operate. It operates by recording audio from the radio, then replaying the audio back into the radios mic port. The drawbacks; Simplex repeaters can only store so much audio, usually only 30 seconds worth, limiting messages to 30 seconds. The second drawback is that your forced to wait for your message to be retransmitted then the unit to store your friends reply before it gets back to you. This isnt too bad during regular chitchat, though it could be annoying, but in emergency situations, seconds can count and having to wait a while for a reply is sometimes not doable. Thus the invention if the RPT-2K.
The RPT-2K is similar to a duplex repeater, in fact thats what it is in a sense, however instead of using high power mobile radios, it uses two low power portable radios. Most times this set-up is used for cross-band repeating which is not allowed in GMRS, however you can use it on two radios withing the same band to make a duplex repeater. You should use a duplexer here as well, however at low power, (.5-1W) the desense is easily avoided and the system works ok. The downside is that your limited to low power, and most portable radios are rated at a 15% duty cycle which means long talk sessions could burn the amplifier out on the TX side of the repeater, especially if you plan to use Chinese radios.
In the end it comes down to how much money you wish to spend and what you plan to do with the system. For me, I plan to use the repeater for camping trips and special events for family and friends to keep in contact. Given the fact that we may go hiking or fishing on the boat I wanted to make sure that should an emergency arise that we could easily communicate without having to deal with dropped cell signals. The setup I have easily covers a few miles so we don't have to worry about signal and it is easily deploy within 5 minutes of getting to the campsite.
