Is there a free Pokémon set completion tracker?

Yes. PullMeter's set completion assistant is free. It covers 24 sets and 4,584 cards. Tick off what you own, or import from your box logger (CSV import and export supported), and it lists the missing cards cheapest-first with today's market prices and the total cost to finish. Your data stays in your browser.

Related: master set costs and cheapest set to complete.