Hey Dax,
Your best bet may be to take your pickup to your local Large scale hardware supplier or Industrial Yard and ask if they have some boiler plate and pipe for your welding bench. Its nice if you can go at least 3/8 in thickness for the table top, since you may find that you will be tack welding projects directly to it from time to time, the thicker is better. the pipe 2 1/2" min dia. can be the leggs. It can be any size you want or even an odd size or shape if you can get a great deal on the metal, be sure to grind a safe radius onto the corners and edges. A nice vice bolted to the top is also a must for home fab stuff.
Remember, especially since your a beginner to do a thorough safety inspection and clear all the flammable stuff far from your new welding operations, this includes lawn mowers, weed eaters and paint if your in the garage.