I think that most of the Zero IF receiver IC's that are available have ADC's build in, so you actually have a digital output. Even without this, ZIF receivers have IQ baseband outputs, where you have 2 analog output's for a single receiver path, which would require a IQ modulator to upconvert this into a Lo-IF approach. It's my impression that "wideband" receivers that cover 150-900 MHz have multiple conversion stages, as well as IF filters, so that they would only work over a subset of that frequency range at one time, perhaps 2 to 10 MHz within that 150-900 MHz.
You might want to look at the Lime LM6002 transceiver part, which would give you a Digital I/Q output, which would possibly be easier to deal with in a signal processing point of view, as you have a single channel of digital information to deal with for each channel.
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.
Best Answer
If I remember right, narrow band FM is used. "Narrow" refers to the small maximum frequency deviation from the carrier center frequency. In FM, more deviation means more signal to noise ratio. Less fidelity is required to send simple digitally encoded signals and voice weather reports than good quality music as commercial FM does. In this case, the deviation is 5 kHz (again, if I remember right).
As for how to build a receiver, that's no different than any other FM receiver. There are various topologies for that. At 160 MHz or so, you have to wake up and design such things carefully. It's not like 1 MHz AM where simple hacks can get reasonable results.