You can obtain a visa to Sri Lanka upon arrival at the airport at the immigration department counter, which is located in front of the passport control desk. The visa is issued on a first-come first-served basis; The cost is 35 USD per person. Children under 12 years of age are issued a visa for free.

More information on how to issue a visa in electronic form and what documents need to be presented at the border control is described on the Visa page on Sri Lanka.

As for confirming the availability of sufficient funds - depends on the mood of the customs officer. As a rule, no one asks. But if suddenly, then a couple of credit cards and a couple hundred of cash is enough.