A brush on waterborne poly will be your current best DIY option. Yes, it will change the color of the wood, as all finishes do. Your limitations on tools and developed skills are going to limit your finish that which you can personally achieve. Adjust your expectations of the finish result to the tools that you are comfortable using. Or set this aside, buy more professional grade tools and materials, and then pick up more practice pieces to learn the tools and materials. Then revisit this project in about 6 months time.

I refinished a wood table in 2014, with water-based poly, as Tanisha Covey suggested. I would guess I applied at least 3 thin coats (I can't remember exactly after this many years). It held up beautifully - it's the only table we have, so it was used for 3 meals a day. Of course we always used trivets under hot things, and wiped up spills immediately, but the finish didn't show any signs of wear.