There's a very low cost CW transceiver for 40m available out of China on ebay dubbed "frog sounds".
For just $19 including free postage you get a decent kit with circuit diagram. I put mine together in about two hours and it worked first go.
The circuit is available via this link. Basically it's a conventional NE612 LM368 direct conversion receiver. The transmitter ads a side tone generator using some NAND gates.
As I've observed before you can't purchase the individual components for the price of the whole kit and the board and documentation is decent.
Update not all smooth construction for some.
John, VK2ASU, sent this:
"Built the Frog Sounds transceiver today. Many problems and many hours spent trying to fix. Have it going to a degree. Getting 1 watt out on 12 volts compared to 3 watts on the previous one.
One major problem I found is that the holes are not all plated through perfect and this stopped the receiver until I found it. The rx works now but "deaf". More time and effort to go.
Decided to do a search on the net if others had problems. Yep!
Here is a link to look at and this.
When you solder a component in make sure you let enough solder to flow into the hole to work right through. There is a hole about in the middle of the board (when it's all built you will find). It is at the end of a track which then goes through the board to the underneath. I had to scrape insulation off both sides and add a wire through it.
For all that the circuit looks really good it's a shame that the board is so bad.
On the plus side the keying is crisp and the sidetone quite good."