Do you have a shop nearby that can let you hear some different monitor speakers? Take some production bounces with you that you are familiar with, if you don't have those, different genres of music that you are familiar with. Would be nice if you know beforehand how they sound on a proper set of monitor speakers.
Then, in the shop, listen to a few of the cheaper models , if your really set on spending little to buy mediocre monitors. Brands like alesis, samson, behringer, fostex, hercules, m-audio have monitor speakers that go for about 60 to 150 a set. 3 to 5 inch woofers. Studiophile 40, mackie cr4, pioneer 50... I'd advise against all of these but if you don't have the money... Why don't you go with bandcoach's advise and head to the 2nd hand store or browse some second hand sites on the net for a hifi amp and passive monitor speakers?
I'd even advise against the KRK 5 inch rokkits. They don't give you a true representation. Of course, you can learn how to work with them if you know their flaws, if you listen to mixes on different sets and in the end, know how to correct for the flaws of your monitors. That is a crappy solution though, but hey, if you don't have the money. But then, you can better go for the cheapest solution that will give you the best bang for your buck. In this case, what bandcoach suggested.
If I could go back in time, I definitely would've put my money aside and waited till I had to spend at least double of what I spent. The rokkits costed me 240 euros. I would've rather spent 500 to a 1000 in total.
Yamaha HS8 for 500 total, Adam A8 for 1000 total. Unless my search would make me able to find a proper set of passive monitors and the amp that goes with it. I had a hard time to find those online. Anyway, good luck with whatever you go for.
Use the search function on the forum if you want to see what else is said about those cheaper monitor speakers. There's a ton of posts about them and there's ton of reviews online that you can find by googling for it.