I want to buy a polarizing and neutral density filter for my Nikon d3000?

But i'm low on money, and the only ones i can afford are made by rocketfish and are 15-30$, should i just wait for better ones or does it really matter

It does matter, but quality CP filters cost $75 and up. Even for a small 52mm thread size (eg. For the Nikon 18-55mm.) This kind of money is justifiable if you're using $1000 lenses, but for budget friendly options it seems wildly out of proportion.

The extra cash buys you a couple of things:
* Good glass. You'd expect that from any filter but I've seen cheap $10 stuff that actually had air bubbles!
* Multi-coating. Coatings prevent degradation of image quality due to reflections (light bouncing back and forth between the filter and the lens elements.)
* Thin rings. An optional feature. Thin rings prevent vignetting, where you catch the filter ring in the corners of the frame. This is particularly useful if you plan on stacking several and filters on top of each other.

So, as usual, you get what you pay for. But don't lose sight of the big picture - don't spend $300 on filers for a $200 lens. The 15-30$ price range (per filter) sounds about right.

If you're also looking for a UV protection filter, I see that Tiffen has a nice UV+CP+and set for $50. Tiffen is a top brand for filters but obviously this is from their budget-friendly line: http://www.bhphotovideo.com/...ilter.html

You HAVE to get a Circular Polarizing filter. I don't mean as in an actual circle… Cir-P filters use a special kind of polarized glass that scatters some of the polarized light out so the camera can function properly. (a normal polarized filter won't work with new auto-focus cameras, the camera won't focus or meter properly… They are meant for old manual focus film cameras)

Hoya and Tiffen are two good quality options that are still reasonably priced, I wouldn't trust any cheaper glass because your not always getting what you think. The best quality filters come from Lee, B+W, Hoya, Heliopan or Canon but can be expensive.

Save up and buy the best you can, although a $150 B+W is not necessary… A $60 dollar Hoya will work fine. If the lens is a wide angle (28mm or less) then you should get a low-profile (thin) filter which will cost more $

Don't forget to get the proper thread size as well (there should be a number on the lens barrel beside with a circle that has a line through it. That number is your filter size in mm)