Hi I'm a new member. Lou is correct CO2 is an excellent choice for your project, dry, safe and cheap. An excellent source for CO2 is a local welding supply store. They will also have the regulator you will need for the CO2 cylinder. You will want one which has a PSIG gauge on it for the downstream pressure you will want to set, do not get the regulator that has flow in CFH or cubic feet per hour. Most regulators will have 2 gauges, one for the pressure in the cylinder which will be about 750 psig, and one for the flow pressure you set. CO2 is sold by weight in pounds from very small 2 pound cylinders up to 75 or even 100 pound cylinders, this is the weight of the liquid CO2 in the cylinder, not the total weight of cylinder and product. Also there are 2 types of cylinders, one for gaseous with draw, the one you want. The other is for liquid with draw, mostly used for fire suppression. Liquid CO2 converts to cubic feet of gas at a ratio of 1 pound of CO2 to 8.7 cubic feet of gas. Probably a good size for you would be a 20 pound cylinder, should last a long time is portable, requires little space. Also remember the product is priced higher at smaller size cylinders. In other words the cost of a pound of CO2 in a five pound cylinder is greater than the cost of a pound of CO2 in a 20 pound cylinder. it takes as long to fill a 20 as it does a 5 and so on. If you see a cylinder on craigslist for sale you will want to know if it is in test, they are tested every 5 years and the date is stamped into the neck of the cylinder. Also make sure it has clear title, verify with a local welding supply they will fill it, many stolen cylinders out there. I was in the industry for 39 years and have seem many people do this.
Thanks
Paul