Electronic – arduino – 2.4GHz Warmer/Colder game based on signal strength

This is a harder problem than I think you realize. The basic Loc8tor system works primarily by virtue of a directional antenna in the receiver, and it doesn't really give you the position of the tag directly, it just indicates what direction it is from the location of the receiver, along with a very rough estimate of how far away it might be.

If you want to create a mesh of automatic receivers, each of these receivers will need to do direction finding, either mechanically by physically spinning its antenna in a circle, or by using multiple antennas and electrically "spinning" the reception pattern. Neither method is going to be simple to implement or particularly low-power.

It is only by combining direction information from two or more receivers (plus knowing exactly where these receivers themselves are located) will you be able to derive an absolute position for the tag.

For data transmission / reception, one of the less expensive options today is a pre-built module around the nRF24L01+ Transceiver IC. These modules typically offer a built-in PCB-trace antenna, 250 Kbps to 2 MBPS bandwidth before error correction, and are tried and tested.

Most important, they save you time in debugging and antenna tuning. After thousands of people have used these modules, which are built on the manufacturer's reference designs after all, most of the kinks are pretty thoroughly ironed out. Also, being able to tap the experience of many others on the internet who have used such a module, counts for a lot when trying to resolve issues.

For instance, this listing on eBay is for a mere US$2.10 with free international shipping. It uses the 2.4 GHz band, which does not need licensing for low power use in most countries.

Another alternative is this 433 MHz band transmit / receive pair of modules (just 9.6 Kbps though), in case you specifically want to stay with transmit-only and receive-only designs. US$1.99 for the pair makes it pretty attractive.

Of course, in each case, you could as well build your own module starting from the IC manufacturer's reference design, and thus learn while implementing your radio functionality.

It is unlikely that the price advantage of massive volume production can be beaten, though.