My preference is thicker. I think the weight of the fabric helps with my training.
In regards to the cost, you might find a nice "pre-thrown" gi. I felt incredibly humbled and honored when one of my sensei gave me my first very high quality, heavyweight gi--one of his own. Depending on the size of your local martial arts community, and your relationship with that community, you may be able to find a really good used gi for a very modest cost.