Going beyond Toadtamer's ignorant and anti-semitic phraseology, his last statement is off on several accounts.
First of all, his $200-250 private driver rate is definitely on the high side. You shouldn't have to pay more than $200 for that even without having to "jew them down". Perhaps the reason he thinks it should cost so much is because the drivers he has worked with in the past took him for yet another foolish gringo WASP and figured they could ask (and easily get) that inflated rate he just quoted.
Secondly, Interbus does NOT want $100 per person round trip. Their rate is $39/pp each way and if you book them through
www.shuttlebus.co.cr it will cost only $37. Grayline is even a little cheaper still at just $35/pp each way. Maybe Toadtamer was just exaggerating those rates a bit to make his private driver rates seem not so unreasonable.
Another thing that he failed to mention is that, because of the limited departure times available with either of those carriers, it would be highly impractical to use them to travel to and from MA in the same day. Interbus has an 8:15AM departure that arrives in MA at noon. Grayline leaves a little earlier at 7:30AM arriving in MA at 11:30. Either way would put you in MA a bit late in the day to go out on a boat. Most people go out in the morning before it gets too hot and possibly rainy, but I suppose charters that have returned from their morning trips would be more than happy to take your money in the afternoon. The problem with returning by group shuttle is that the last Grayline shuttle leaves at 1PM and the last Interbus shuttle leaves at 1:45PM, meaning the most time you would have in MA if you were trying to do it as a same day r/t by shuttle would be 2.25 hrs, hardly enough time to go out fishing let alone justify the 8 hrs of r/t driving time.
Obviously if you have a private driver you'd have much greater flexibility with times. However, it would still be virtually impossible to drive to MA and arrive at a reasonably early enough time to go out on a morning boat unless you were prepared to leave SJ WELL before dawn. The return trip by private driver might fit better into your schedule because you could leave much later in the afternoon but correspondingly that would put you back in SJ well into the evening and probably pretty worn out for much mongering after a full day out in the sun and 6-8 hours on the road. The only semi-practical way to do this as a 1 day trip would be to fly one or both ways or possibly to use a driver only for the return trip. And if you go that route you could do just a half day fishing trip and return by shuttle for much less than what you'd pay for a driver and still have the time and energy to enjoy your evening back in SJ.
Of course, your options open up considerably if you're prepared to bite the bullet and stay over a night in MA and that is probably the only real practical way to do this trip unless you're prepared to bite the bullet for airfare. Even for an overnight fishing trip to MA, you still might want to fly one or both ways. I already explained the limitations for driving to MA (whether by private driver or group shuttle) and arriving there early enough for a reasonable day of fishing the same day. Nature Air has a morning flight that will put you into the local airport in Quepos around 9:30AM but for the earliest arrival you'll need to fly via Sansa which has a flight as early as 6AM.
Alternatively you could leave for MA as late as you want by any method you want as long as you're content to just do your fishing the following morning. The group shuttle companies also have afternoon departures, if you wanted to get in a late morning MP session before you left for MA and/or didn't want to pay extra for airfare or a private driver. And if you wanted to make day 2 a fairly full day of fishing and yet still get back to SJ reasonably early in the evening, the last flights back to SJ leave around 4:30PM. If you can get Nature Air's "loco" fare (~$55/pp o/w), that would be much quicker and even a bit cheaper than hiring a private driver to take you back from MA even if there were 2 people in your group. If you get stuck with the regular fare (~$75/pp o/w) it would still be much faster than driving and not that much more than using a driver for 2 people.