The Sinclair ZX81 was launched in March 1981. It had a Zilog 80 CPU running at 3.5MHz and a rather tiny 1k RAM with 901 Bytes available. This could be expanded up to 64k.
The keyboard was touch-sensitive and was considered to be a big failing on userbility. Its one big selling point was the low cost. £70 would buy you one of these, which is £300 ($400) in 2019.
It achieved such a low cost because of its design: Simple. It uses only four IC’s on the tiny circuit board.
These photos below show the ZX81 in Kit form. This was a cheaper way of obtaining one, the built-it-yourself kit cost only £50, which is £210 ($270) int 2019.