You can reach Nicaragua on different budgets and times. We went on one somewhere in the middle option. I'll explain the details below.  

Booked ticket at the bus terminal from the shopping Mall in Monteverde. The bus is leaving to La Irma  at 4:20 AM. if you are on the route of the bus they will pick you up from the hotel but you need to let them know in advance . Price is 1050 colones per person (approx. 2$). 

After 2h, the Bus drops you off on the PanAmericana. Cross the 'street' as you need to get the bus in the other direction. 

Here you can take any bus going towards Rivas (Just make sure it does not pass Nicoya). You can either get another bus to Penas Blancas and from there one to Rivas or get into a Tica or Transnica bus which will bring you directly to Rivas. If you want to save some time and have some money to spend might be better to get one of these buses. We took the Transnica (as it came first) it was 20$ per person.  This option also saves you some time at the boarder as they arrange everything for you.

There are several reasons why you would want to visit Monteverde. We actually went there for main 2 reasons: 

We heard a lot of people talking of how amazing the experience of "flying"/ "hanging" over the rain forest is so we said we should take the chance of being in Costa Rica and book the Tour offered by 100% Adventure.

The Canopy  tour was 45$ per person and included:

• the equipment (you can get a helmet on which you can mount a go pro
• supervision stuff
• 5 canopy lines (if I am not mistaken)
• one rappel 
• 2 supermen (including the 1590m long one)
• one Tarzan Jump 
• possibility to buy pictures 

After a intense start of the day and hiking Cerro Chato (HERE details) we left to Monteverde. 
There is a TAXI - BOAT - TAXI  trip that brings you to Monteverde. As far as we checked online, ideally you should book one day in advance. One of the companies that are available is Anywhere Costa Rica . We did not book them in the end as we found a cheaper alternative through our hostel 
(Cabinas Las Palmas).