$100 for a DIY CO2 system is absurd to begin with. If it's using $5 a week in supplies for a 2-liter aquarium, then doubly absurd.

This is the $25 (plus about $1.50 per month in supplies) DIY CO2 kit that I use on a 5-gallon aquarium, and I highly recommend it for small aquariums if you don't want to go all-in on high-pressure CO2: https://www.amazon.com/Clscea-Aquarium-Generator-System-Diffuser/dp/B0BL92SGW4/?th=1 Each charge lasts about 3 months at one bubble per 5-8 seconds. You will also need 2 2-liter soda bottles, citric acid, baking soda, a gram scale, and a milliliter measuring cup.

Plants and algae don't actually "compete" for nutrients in the water column. I think it was Tom Barr who debunked that concept. What's needed is a situation where conditions for the plants are optimized so that their own anti-algae systems can kick in. Oxygen is actually toxic to simple-cell organisms, so getting the plants optimized will poison the plants' surfaces, and eventually the water, against algae by saturating them with oxygen. Let the oxygen kill the algae, and, as others here said, stop the Excel.

Consider CO2 injection. This is the $25 citric acid/baking soda DIY system I use on a 5-gallon tank. I run it 24/7 at about 1 bubble per 10-15 seconds and it lasts about 3 months per charge. You will also need 2 2-liter soda bottles, citric acid, baking soda, a gram scale, and a millimeter measuring cup. Caution: Some fish, like Endlers, may not tolerate constant CO2 injection, so observe as you go. My Betta does fine, but the Endlers eventually developed shimmy.

https://www.amazon.com/Clscea-Aquarium-Generator-System-Diffuser/dp/B0BL92SGW4/?th=1

If you don't want to inject CO2, then consider the Walstad lighting schedule. Not the full dirted tank thing, just the lighting schedule. 3-4 hours on, 4 hours off, 3-4 hours on. The thought there is that water has a natural amount of CO2 in it that gets depleted in 4 hours, so the mid-day 4-hour siesta allows the water to take in more CO2 from the atmosphere for the second lighting period. Her tanks are low-light, so if you can adjust the intensity, turn it down.

You don't say anything about NPK macronutrients. If you want to go cheap, I use the Jobes 13-4-5 (N-P-K) sticks for houseplants. Break them into quarters, place some pieces under the swords and other rooted plants, then place a quarter (or more once you get it dialed in) on the surface at the back. Measure nitrate and do water changes if necessary to keep it around the 10-20 reading.

I do 20% water changes twice a week, so I am a believer in that. I top it off with distilled water to prevent mineral hardness buildup.

Once you have all that optimized, add a bunch of fast-growing plants. I like hygrophila difformis (water wisteria) for this because it's usually forgiving of water parameters and grows like a weed. Hygrophila polysperma and dwarf sagittaria are also generally easy. Figure out which plants like your (optimized) situation and grow those.