Yes... And if you are actually thinking about bitcoin for the long term, such as 4-10 years or longer, then your average cost per BTC will not matter so much because you are not planning on selling any time soon.  At the same time, maybe after 6 months, 1 year or 2 years, you might get to a point in which you have already accumulated a decent amount of BTC, and you might start to consider if you might want to attempt to be more strategic in regards to when you buy.. but even sometimes those people who are overly trying to be strategic about their BTC buys, they may well end up with way less BTC because they are spending more time waiting rather than actually buying.  You have to figure out what works for you, and surely there is no turning back the clock if you might have had some opportunities to buy BTC, but if the BTC price does a step ladder kind of a move upwardly, and it does not come back down and then you might be thinking that maybe you should have had bought some rather than waiting..

and sure, you do not have to buy with everything that you have, yet even waiting with some of your value (and holding it aside for  potential dips) is a choice that may or may not be a good idea.. but that also may well depend upon your own situation and sense of satisfaction with the amounts of your buys.  

Even our hypothetical poor person given above, many of the times he ONLY has $100 per month to be able to buy bitcoin, and that is if his discretionary comes in consistently in the regular way, but he is also going to have months that he has extra and other months he does not have enough, so those are reasons to make sure that his reserves and his floats are in a good place (and yeah, of course, I am presuming the emergency funds is also there, but the emergency fund is not being used for the purposes of filling in the variance of income/expenses from month to month). .. so if we assume the guy has all of his finances in order in regards to the reserve and float, that still may well leave him with the $100 per  month and questions about if he should use all of every month for buying BTC or maybe he might want to hold some in reserves.. but even if he had ONLY been buying bitcoin for a year or two, then he might have had only bought $1,200 to $2,400 worth of BTC during that time, so there surely still might not be enough BTC stacked up for him to really feel comfortable in waiting, and it might not even matter so much about the actual BTC price, and maybe he has to wait until he gets to around 4 years or more investing into BTC when he had invested $4,800 or more into BTC when he starts to feel that maybe he can start to become a bit more strategic regarding when to make his BTC purchases... .

and another thing is that investing $4,800 over 4 years, some of those purchases may well be more profitable than others, and maybe it is not ONLY the earliest purchases that are the most profitable, but there might be some recent purchases that are not very profitable, but having all of that in bitcoin, then at least the BTC is there, so that in the next 4 years, you have whatever you had during the first 4 years that had been able to grow completely (as long as you were not fucking around and withdrawing any of it) plus you wil end up having whatever new value that you ended up putting into bitcoin after the second 4 years, so maybe there will be various points in which you are able to increase your disposable income during that time, so maybe after 8 years, you might have more than $9,600 invested into bitcoin.. depending on your own abilities and/or luck in regards to your financial situation and your managing of your circumstances. including managing your bitcoin holdings and including perhaps having some appreciation that it could well end up being that some of your abilities to focus on accumulating BTC in your earlier years ended up giving you more options later down the road, so long as you did not end up losing whatever coins you had accumulated.