"If you can manage, buy them all."

Without more context, it's a little bit hard to tell exactly what was meant, but it sounds like it tried to express the idea of "If you can find some way, try to buy them all" or "If you are able to afford it, even if you have to cut back spending on something else, buy them all." It suggests that the person was able to come up with just enough money to afford them all, even if it was not easy. In other words, I think you are right in your second suggesting, overcoming a difficult situation of a lack of money.

Other contexts where the verb "to manage to do something" is used would be, for instance, "Even though I was very shy, I managed to give a speech at the conference." In this case, the person found a way to overcome the difficult situation of fear of public speaking, perhaps still feeling hesitant, but finding just enough courage to be able to do it, after working hard to calm her fears.

In another example, someone might say, "I broke my leg last year, but last week I managed to run a six-kilometer race." The person probably did not win the race or even do very well, but he overcame the injury he had and was finally able to run again, after lots of work and exercise.

I hope that helps! :-)

English writing ,12 February 2017