From the things I understand about there reasons of not being able to buy Bitcoin is actually the price so there is no strategy that will give them a lower rate of buying price of Bitcoin because any price it has is what everybody who wants to invest in Bitcoin will buy, meanwhile is mostly after buying you can be asking for strategy, unlike before alot of people were inexperience of knowing how to navigate into strategies that will make them moderate on there investment but now there are strategies people has been talking about they usually use on Bitcoin, I don't no if you have heard about DCA but you can read about it to no more because I no is a strategy for a lot of people.
Someone can buy bitcoin in any amount from 1$ upwards. So you can just invest any amount you think he will be better for you and ready to risk.
Because of financial strength differences ways at which people can still invest on Bitcoin was talked about and also how they can use small amounts to starts with but however that doesn't really mean that someone can use any amount, although is not that using any amount on Bitcoin is wrong but the process of changing it into Bitcoin will be problem because for this amount of $1 you mentioned is actually way below the average someone could use, it might not even be possible to convert it into Bitcoin because after everything It will not be up to $1 again, so actually my point is that no matter as little as it is someone should do more better than $1.