What is a "lauda"? Is it equivalent to a page?

No. If you look it up in the dictionary, you'll see that "lauda" means simply a printed page. It is a measurement just as accurate as a "bottle". How much do you pay for a bottle of soda? You can't tell without specifying the volume, right?

Likewise, there are "laudas" in various sizes. Some book publishers work with 2,100-character "laudas", counting spaces as well.

For Public Translators, one "lauda" refers to 25 typewritten lines. As the law that sets this size dates back from 1943, it was long before the computer age. I don't know about the other Brazilian states, but in 2003, for the State of Sao Paulo, JUCESP determined that a 1,000-character "lauda", not counting spaces, would be equivalent.

Therefore, it is not possible to determine precisely in advance how much a sworn translation will cost, however a rough estimate can be attempted. Most computer programs are capable of telling instantly how many characters without counting spaces there are in the translated file, so it's a matter of multiplying by the correct listed rate. The first "lauda" or part thereof is charged as one "lauda". Afterwards, the total cost increases at every one-tenth of a "lauda".