Not as simple as you told, what if you buy at higher price and then price going lownfor several months/several years? Waiting price for going back? It easy if you spend small amount, let say below $50K. But what if you spend more than $200K
Sorry... but I'm sure someone must have said "buy with an amount you can afford to lose"... then if $200k makes you regret and even get depressed when you lose that amount, I think that's too big an amount to spend on Bitcoin.
Perhaps a more suitable investment model is safer than Bitcoin if one adjusts for the fears that occur.... Bank deposits look more appropriate for him, that is if the owner of the money can live on $833 per month (assuming the APY is 5%. .. the numbers could of course be bigger)..
For BTC purchases, usually after doing DCA and someone's portfolio value experiences a profit... that will make someone love investing. It's possible to do DCA from tens of $ per week.