Sorry if I am repeating an already frequently-sought question, but I searched google several times and could not find anything relevant to my project.
I want build a wireless mailbox mail detector for mymailbox which is located about 30 meters away from my house. In terms of line of sight, the signal has to pass through 3 houses. The sizes of the data being transferred is minimal and speed is not a priority. Most importantly, I would like to find the cheapest possible solution for this as I am on a very low budget. So basically something that will get the job done while keeping the price low. At the moment, I have no idea how much something like this would cost, so I dont have a budget. Any suggestions are appreciated. Thanks