it depends on what type of plants you plan on growing. if you're going for high light demand plants, you will definitely benefit with going pressurized, especially with your tank size.
i agree with orlando, go with the largest co2 tank that you can afford. you can get one from either a fire extinguisher supply shops or (where i get mine) from a beverage supply shots. i prefer a beverage supply shop, because after the initial cost for a tank, when your tank is empty you just return it and swap for another. and you only pay for the cost of a refill.
the initial cost to set up a pressurized system is daunting for people of limited means, but you do save in the long run. with a 10lb tank, you would have to replace/refill every ~6 months, as opposed to every 1-2 weeks with DIY.
good luck!