I do not know what country you are from but each country as limits on the amount of power a transmitter can radiate in a given band. They also specify which band can be used for what type of service.
The obvious is the more power the greater the distance; however To prevent interference with other units on the same frequency the range is limited by the amount of power allowed in a particular band for a non licensed operator. This is generally in the milliwatts.
Different types of modulation can help increase the range. There is also using SSB Single Side Band, amateur radio operates are familiar with this.
To the best of my knowledge the 5K range you want will not be reliable with the allowed power unless you have a very good receiver in a low noise area.
My recommendation would be get a amateur license if you want to build it or get a piece of commercial gear designed do the job. That equipment would also be licensed.