The good news is you won't have any transfer taxes, this is one reason people put real property in a company name - it makes a good selling point.
I am not sure what the lawyer charge, but I am guessing something similar to his or her normal fees, since the due diligence is almost the same. The lawyer not only has to check into the property's records, but also the company's records. You will want to look at this article for some things to watch out for when buying
an existing Costa Rican corporationThis article
Costa Rica land for sale transfer fees shows the fees involved in a normal transaction, so you would just discount the 3% transfer tax on the registered value, which will leave you paying the 1.25% or so of the lawyer's fees plus the stamps involved in transferring corporate shares. You can probably calculate close to 1250 dollars for each $100,000 of property value in this type of transfer, depending on the lawyer.