At least to cycle If you have the bio balls already then definatly use them, IMO they are one of the best things when going through a cycle. After that if you want to remove them do so slowly, a couple of hand fulls a week.
If you can't afford "enough" live rock then use the bio balls and as Kip says use a prefilter cleaned once a week.
You can forget that Nitrate factory trap CRAP, because it just isn't true. Although the end result and function of the bio balls will leave nitrates and not break them down is true enough, the same holds true of any mechanical filter, canisters, UGF, saddle filters, powerfilters, sponge filters...all of them. Even a DSB if not properly maintained can be a nutrient sink that can be accused of being a time bomb waiting to explode or so they say, and say, and say over and over again. Keep in mind that every SW Hobbiest will have to have a plan to export the build up of Nitrates...ie Water changes, DSB, denitrator coil, nitrate sponges..etc..
Regular maintinace will take care of ANY such problems in a wet/dry with bio balls. There your balls, protect them with a prefilter, keep them clean, and they will serve you well.
On the other side of the coin, many will not use them and try to go for a more natural way of reef keeping. Like the DSB, refugium, Sump with live rock/ macro algea. Once again many choices here. Up to you to map out how your system will be setup.
Bottom line--- Many ways to setu up a tank. You weight the options. The goal is the same. A great tank.
Thomas
Why must I always get emotional about these things.