Yes, you can cut plexiglass by hand using a sharp knife or blade (utility knife, box cutter, glass cutter, etc.).

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.

The cost to weld aluminum averages about $14 to $22 per pound. The type of metal factors into the overall cost of any welding project due to the cost of the materials and the expertise required to work with it. Some of the most common metals used by welders include:

• Magnesium alloy: $7–$16 per pound

• Low-carbon steel: $11–$12 per pound

• Stainless steel: $13–$15 per pound

• Copper/brass: $24–$29 per pound

• Cast iron: $38–$79 per pound

• Titanium: $60–$85 per pound