 Selling the ZX81 over the counter was seen as something of a gamble and Rowland 's colleagues were initially unenthusiastic about the scheme . Branch buyers thought that the ZX81 was unlikely to sell more than 10 – 15 units per branch at launch . Rowland himself thought that the ZX81 would sell about 10 @,@ 000 units during the first five months of the retail agreement , equivalent to one month 's mail order sales by Sinclair . In the event , the ZX81 was a massive success for Smith 's , it went on sale for £ 99 making it the first home PC in the UK to retail for under £ 100 . The " Computer Know @-@ How " sections were swamped with eager customers , overwhelming the 300 staff who had been trained to demonstrate the machines ; a Financial Times correspondent wrote of being " dazed and bewildered by the crowds of schoolchildren clustered round the ZX81 in your local branch of W.H. Smith . " Within a year , Smith 's had sold 350 @,@ 000 ZX81s , making an estimated net profit of £ 10 million . Sales of peripherals , software , books and magazines netted even more profit . 
