As of 4/2012 there are new rules and costs for boats that check in/out of (Rio Dulce) Guatemala
To check in and out within 3 months is Q2600 total (approx $330 USD).
You can extend your 3 month permit
for another 12 months for Q1800 (approx $230).
At the end of the 12 month extension you must leave Guatemala
for 90 days (until this year it was 72 hours)
There is no longer a 'per day' fine for an expired permit
. If you fail to renew your permit, allow your permit to expire it is a $500 USD fine or the option to import
The above is information provided by the local agent and include his fee. Of course doing it yourself would be a few dollars cheaper.