Assuming you have a good product, the best way to deter pirates is to set a reasonable price so that people feel they are getting value for their money. The lower the price, the less people will want or need to evade the cost. There are studies showing the price points where you tend to meet increasing resistence, although I don't think they have much data on the sub-$10 field.
Having a free trial period with limited time or limited features would probably help to ensure people can feel good about spending their money.
Offering support would help also.
Free updates would also be a plus.
Any sort of serious DRM will turn people off for low cost products, but some sort of protection (serial number tied to user name?) will be necessary if you offer a free trial.