I'm a US passport holder. Next month I'm planning to visit Prague to see my girlfriend and I'm hoping to be there from beginning of July to end of August. I'm going to buy roundtrip tickets at once but I don't know if they will ask for sufficient finance. If they do, what can I use as proof and how much will I need? I thought I could get something signed from my girlfriend and her family to be able to suffice for me but is that even possible?
For US Citizens who are traveling to the Czech Republic for up to 90 days as a tourist or for business purposes do not need a visa.
However, to answer your question directly:
Generally, there are several recognized ways to prove your financial sufficiency:
A personal bank statement indicating your financial movements (for at least 3 last months)
Proof of employment
Supporting document to attest sponsor’s readiness to cover your expenses during your stay
Proof of prepaid accommodation
Document about accommodation in private
Proof of prepaid transport