Cutting rectangular ductwork requires careful measurements and the right technique. Use a measuring tape and pencil to mark the cutting lines accurately. Tin snips are excellent for straight cuts on smaller ducts. For more extensive or thicker rectangular ducts, a reciprocating saw with a metal-cutting blade is effective. 

Ensure the duct is well-supported and secure while cutting to prevent wobbling and maintain precision. After cutting, use a metal file to smooth any sharp edges, ensuring safety during installation. 

The average cost for a welding project is about $300, with typical costs ranging from $125 to $490. However, prices can be as low as $125 for very small jobs or exceed $1,200 for large or complex projects. Welders typically charge an hourly rate between $65 and $150, depending on their experience, and many charge a minimum fee to cover overhead and travel expenses. The total cost is influenced by several factors, including labor, the cost of materials like metal rods and shielding gas, the type of metal being welded, the project's size and complexity, and your geographic location. For a precise quote, it's best to ask a local welder for an estimate based on your specific project.

Since water heaters are primarily made of metal, they’re commonly accepted by scrap yards and collectors. Don’t expect to fetch a high price, though—water heaters are mostly steel and aluminum, which aren’t high-value metals. Some components are made of more valuable metals, like brass and copper, but they’re a small portion of the heater and won’t affect the price much.

Professional metal fabricators typically charge around $70 per hour, but the total cost of your project will depend on several factors. The largest cost drivers are the size, complexity, and design of the project, as well as the price and type of metal used. A good way to estimate the total cost is to multiply the cost of raw materials by four; typically, one-quarter of the total goes toward materials and three-quarters toward labor. Your geographic location can also influence costs, as labor and material prices vary by region.