Do not worry...it is possible and you can do it everything on your own...you do not need any middle person to book anything for you...even you can ask directly for good deals.
I'm with you why follow anybody timetable...?
1-Hanging bridges you can go there almost any time during the day and pay the entrance fee in person ...ask for a good deal..
Same day you can drive to La Fortuna waterfall and pay the entrance fee...anothe good saving!
2- Any where around the volcano could be nice place to see it...even pay at Los Lagos and hike inside the property...or El Silencio, or drive to the bridge on the way to El Castillo...
The same day later on the afternoon you can go to some of the Hot Springs...like Eco Termales...if you can make the reservation early in the morning...fo me the best time is around 5:30PM with dinner included!
Again you do not need any middle person you can book everything yourself...you will even save money!
I have been visiting Arenal and even I spend 5 years of my life living there...nice people and try to deal with local people incredible nice educated people!
roadadvisor from Costa Rica and in Costa Rica
Let me know if you have any other question....