And in the least elegant, but cheapest, form factor WaveShare make a module they call the Core51822[1] that is cloned by tons of folks and is basically the generic nrf51822 module you'll find for ~$5 on ebay. It's the most awkward compromise of 2mm pins (and in double rows too) that make it wholly incompatible with a breadboard yet it's also bigger than any other "embedded" module. But there's also a BLE400[2] "motherboard" which breaks the module's pins out to 2.54mm-spaced connectors, along with a few LEDs and buttons and a USB serial chip (all of which can be disconnected via jumpers), and one of those old, giant, 20-pin JTAG connectors.

It's not able to plug straight into a breadboard, but it does allow full access to every possible IO pin on the chip, and it's probably the cheapest setup you can find. A combination of a Core51822 and BLE400 seem to be easily available for ~$15-$20 shipped, there's even stock available through an Amazon Prime seller for $22.

If you do go for cheaper options, keep the chip differences in mind. The nRF51822 is currently available in three variants, and the differences are big. AA has 16K RAM and 128K Flash, AB has 16K RAM and 256K Flash, and the AC has 32K RAM and 256K Flash. The AC variant was only introduced recently, so some options might still have the older/cheaper variants. But some examples and tools (such as Nordic's BLE sniffer firmware and tools) are starting to require the latest chip with the 32K of RAM, so make sure whatever you're buying explicitly promises you'll get the 32K RAM chip (the AC variant), like this OSHChip does.

[1]: http://www.waveshare.com/wiki/Core51822

[2]: http://www.waveshare.com/wiki/BLE400