1 cheap way to reduce air bubbles in your casts is to dust the mold with baby powder prior to pouring the resin. For molds, follow Glassman's tutorial
and pour the rubber s l o o o w l y.
Another way that I haven't tried yet is on Sarge's website
, and looks like a good way to make fairly bubble-free molds.
I have been trying pressure molding/casting lately and have had good results so far. All the equipment cost me about 60 dollars. The only drawback to using a pressure system is it takes a lot more time to build a mold box, at least with the method I've been using. This list of parts is what Master Gunzz recommended, and what I use:
Pressure Cooker: Presto 6-quart - $45 with shipping from amazon.com
Tire Valve: Generic brand - $3 at Wal-mart
Silicone Caulk: Clear kitchen caulk - $4 at Wal-mart
Tire pressure gauge: Generic brand - $2 at Wal-mart
Tire pump: Any pump, I use the kind that stand up and you push up and down, as it'd take too long to use a small hand pump.
You take out the rubber stopper in the lid and put the tire valve in it. Then you seal around the valve and metal piece in the middle of the lid with the caulk. When you build the mold box and fill it with the rtv rubber, just place it in the cooker, close it, and pump it up to the desired pressure. Bantha5 once mentioned that he pressurizes to 40 psi, so that's what I use and it works well.
As for the method I've used to build the mold box and cast the part, the guys at Goregoregore.com
have some good tutorials with pictures and all.