I wouldn't spend time trying to add to your tent - consider erecting another tarp shelter adjacent to or above yours. This would add a lot of dry square footage for a relatively low cost. You're in effect making a giant vestibule in front of your tent.

On the low end, you could get a cheapie backpacking tent like https://www.amazon.com/RainFlyEVOLUTION-HAMMOCK-WATERPROOF-Survival-Bracelet/dp/B074BTJMHJ/ and stake it out with some cheap steel poles like https://www.amazon.com/Mountainsmith-Steel-Tarp-Pole-Silver/dp/B01N2RM2L6/

The poles are heavy and a bit bulky compared to some alternatives, but they're also cheaper and super sturdy. If cost or weight is more of a concern, the telescoping aluminum ones are OK, but they seem more prone to bending, especially at full extension. I've heard some people use telescoping painter's poles to stake out tarps, but they're usually steel and it will require a bit of DIY to get them set up correctly.

If that's outside of your price range then consider buying a larger hardware store tarp and staking it out over your tent like a rain fly. You'll get a lot less height and floor space, but it will cost like a third of what the above option costs.