As far as I know one of the best modeling tools out there are:
1. Alias Maya
2. 3d Studio Max
3. Lightwave

These are the 3 that I had a chance to explore. I was getting quite profficient with 3dMax, however, due to the decline in popularity Max yielded its way to Maya. Maya is my favorite at this time, although I am still novice at it.

I am 100% with Drake on the ability to gain softies. There have always been ways and there are even more ways today of getting your hands on some copy. If you don't have your "evaluation" copy yet, it means that you are either not looking hard enough. Emule, LimeWire, Kazaa and other peer-to-peer exist to aid the poor people.

Back to the topic. My first choise would be Maya for a modeling software.

Hi Alejandro,

Based on what I saw in your portfolio I guess you might know that first you must realise what type of designer you want to be? As for representing your ideas in 3d and rendering you can consider almost any 3d packages from Max, Maya, C4D, Softimage, Lightwave ... to Amapi Pro and Rhino as reasonably affordable choices. Based on my own experience they are all fairly easy to quickly build a 3d model which can show your idea in a decent way I guess you may have enough engineering understanding of what can be practical. When you realised the Nurbs modeling is the only way to go you may look into Maya and Rhino and Amapi as the better choices also Softimage and Max have Nurbs modeling tools too. Rhino is a better Nurbs modeler and the only one let you evaluate your curves and surfaces quality and curvature the drawback is that it doesn't have construction history as in Maya. I was using Maya and Rhino in early days for concept modeling. But if you look further and want to be a true designer which can develop a manufacture-ready concept then you must look into pure advanced surface modelers and high-end cad packages like StudioTools, ICEM, Imageware and Unigraphics NX, Catia. You should consider that you or your client going to use which package for their final stages. They are not cheap and easy to learn but essential for today's advanced designs.

Good Luck