Huuuh, where to start? So, the prices here are, let's say, like in Croatia, in Zagreb. Some of them are lower, and some of them higher but nothing much, in general like in our country.
What to see? Make a list... Alfama and all the viewpoints around including Castelo de Sao Jorge, city center (Praça do Comércio, Baixa/Chaido, Miraduoro de Santa Catarina, Elevador Santa Justa ...), LX Factory, Belem, Sintra, Christo Rei, Cascais, Costa De Caparica... that are just highlights.

You must try bachalau (codefish) and pasteis de nata...

I don't know the prices of regular taxi, but Uber has quite fair price so try use Uber or just public transportation (1,5 euro). For longer distances see if you can find something cheap to rent or use the train.

Hope it helps... ;)