If that is his cheapest option and if he truly has cheap electricity bill which I would define right now up to 0.05 and for long term like your friend is looking a maximum of 0.07 cent would be the max limit of what can be considered "cheap" electricity compared to us in Europe which the prices have skyrocketed and most likely we will see further increase this very September.

6 such cards would cost him like 900 dollars plus 200-300 dollars for used other parts that would be 1200 dollars for a 6 cards rig,of course he should get a very good PSU that may rise the cost but it will be worthwhile in the long run,so for 1500 USD he can buy the parts himself or from what I have seen in local market where I am plus in Ebay and others you can get a rig with 6 such cards in the above mentioned price.It can be as jump starting for your friend,if he likes what he sees and start to thoroughly understand cryptos even more,I am sure he will expand.