What OGBama is saying is that if you're "in" this, get used to the idea of spending, and you really do need both, if you're going to get the most out of your production experience.
On the other hand, to your point-- _IF_ you are working exclusively "in the box" for now, with no need or desire to bring in any audio sources (vocals or other live instruments) or MIDI, and you are using just samples or loops or soft-synths within whichever DAW is your platform, then I would say a good set of monitors would be the next step (assuming you are looking at active/powered speakers rather than passive, otherwise you'd have to buy an amp as well).
If you spend a little more on good speakers now, you won't need to upgrade later, and with proper care, they should serve you well for years.