Several ideas I have used
1) kimkim is an excellent site most never heard of. They have plans from 3 days all the way to over 20 days.
2) Many major cities have free walking tours. These are 2-3 hours tours by pro guides and you pay at the end what you want and it's much cheaper. We take all the available tours.
3) Warsaw have milk bars, a must visit. These are restaurants from the Soviet era. Very cheap, simple Grandma food and very tasty.
4) Both of these countries are amazing, and we love Eastern Europe. The food is great too. We ate perogies many times in Poland.
5) Frommer is another site with 1-3 weeks details plans what to see in each country.
6) Use booking.com and get excellent B&B. You want to immerse in the local culture and try what the local like. Don't be shy and ask the locals for help. People love to help. We never used organized tours, you can't experience and feel the local culture.