San Ignacio to Tulum

San Ignacio to Chetumal -- try the Marlin Espadas bus. A bus departs from Flores daily at 7:30 am and makes a stop at San Ignacio on the way to Chetumal. I don't have a lot of details about schedules or where to meet the bus, but here's an email address and some links...
marlinespadasltdbelize@gmail.com

http://marlinespadas.com/

https://www.facebook.com/Marlin-Espadas-M%C3%A9xico-SA-de-CV-911522482202854/

I'd guess that you would arrive at Chetumal in mid-afternoon. An ADO bus from Chetumal to Tulum takes 3.5 hours, and there will be some waiting time for the bus.

Another option... Get a bus to Belize City (leave SI around 7am), and get the ADO bus to Cancun -- it leaves from the bus terminal at 11:00 am and makes a stop at Tulum. You should arrive at Tulum around 5 or 6 pm.

Second option sounds the best! Are the buses that run from SI to Belize city the local Belize buses? Thanks for your help!

Are the buses that run from SI to Belize city the local Belize buses?

Yes -- old school buses. I'd allow 2.5 hours for the trip.

Awesome you have been super helpful. One last thing, we are travelling from cancun to Belize city also and have pre booked the tickets through ADO. I have read that there are charges for crossing the border into Belize. Does this still apply with pre paid tickets? Which currency is it paid in and can it be paid by card?

There should be no border crossing fees, but that doesn't stop the infamous scam at the border.

First stop is Mexican Immigration and they will ask for money -- 500 pesos, or maybe 533 pesos now. If you flew to Mexico with any airline except Thomson/TUI/First Choice of the UK, then you have already paid the Mexican Tourism Tax, so you do not have to pay anything when you leave Mexico -- there is no departure tax. You can argue with the Immigration officer and see who gives up first, but I carry a recipt from the airline which shows payment of the Tax. The officer keeps a copy and I haven't yet paid the scam. If you have to pay, they will take pesos or USD -- don't know about a card, but I doubt it.

I don't know your nationality/passport, but for most, there are no fees when entering Belize. There are departure fees that amount to BZ$40 (or US$20) per person.

If you're travelling from Cancun to Belize and then back to Mexico, you will have to pay the Mexican Tourism Tax again for your second trip to Mexico. I've never paid at the border upon entry to Mexico -- I pay at Cancun airport upon departure from Mexico.

Amazing knowledge! Thank you so much for your help!!

It seems that it’s a different company that manage the return journey from Belize City to Tulum. Do you know which company that is and whether the busses will leave from the same station in Belize City?

Unless something has changed recently, the buses are ADO buses but apparently the trip from BC to Bacalar is "operated" by Belizeans -- that's why the run doesn't appear on the ADO website.

The buses depart from the main bus terminal, still known as Novelo's, in BC.