Welding is a trade that is subject to the vagaries of the construction business. More technical welding on materials like aluminum are more subject to the vagaries of the manufacturing sector.
Many of the welding positions are unionized which provides better benefits, but those positions are reducing as the sectors contract.
I suggest you research online for the requirements needed to get certified in the area of welding you're interested in. Then see what you have to do to take the certification test. You may be much better off buying a rig, getting some scrap, and teaching yourself when compared to the cost of the trade schools.