MacroP: Where did you get your prices from? The prices on the website seem a fair bit higher...
Check out the order page. The 2E0 has the integrated AFR display. The 2E0 DIY kit without a sensor is around $200-$230 and a suitable 7057 sensor is $90. The prebuilt units are around $500 with a 7057 sensor.
I have the 7057 sensor connected to 2A0 version which I built.
My display is a seperate device.
I will say though to all, again, that these kits are very hard to build. They are small and very complex. If you're not right into electronics buy the pre-built unit.