cutting frame

This is probably a common argument about BD's but once I cut the frame I would want to use new metal all the way back. What does 2x4 or similar steel like that cost? What size sheets of 3/16" or 1/4" can I buy ($?)

 

i just got some 3x3x1/4 square tubing at work, it was $8 a foot. 2x3 works good on trucks and would be cheaper then the 3x3 mentioned above. 3/16 and 1/4 is commonly availabe in 4'x8', 5'x10', and 6'x12', its hard to say on price because the cost of steel constantly fluctuates. if i remember right the last time i ordered a 4'x8'x1/4" it was just under $300.