How good and widely available is public transport/buses? I have travelled around Mexico, Central and South America using buses, but not for day-to-day transportation. I'm thinking of if I reside in a town such as Grecia or San Ramon.
Okay, I don't know Grecia but in San Ramon there are no buses that travel from one part of town to another, but it's not that hard to walk from one end to the other, it's small, maybe a mile from north to south, at most.
If you are asking about buses to get to other places, there are 2 main bus stations, one that goes "everywhere" and another that has buses to Puntarenas and San Jose, with regular direct buses to San Jose. Although they are not really direct - they stop here and there along the way; but much fewer than the non-direct buses.
As long as you live very close to the main part of town you don't need a car. Even a taxi a couple times a week would be cheaper than owning a car. But if you live 3, 4 or more miles from the main part of town, taxi use may be more or perhaps the same as owning a car depending on how many times a week you need to go to town.
I live about 7 miles from town and I have calculated that if I used a taxi all the time and went to town once a week, it would cost me about the same as owning a car (per month), when you factor in repairs, RTV mechanical check required each year, new tires and brakes, gas etc (but not factoring in the original cost of the car).
But since it's not significantly cheaper, I decided to continue to keep up the car instead of using a taxi because it's more convenient and can be used quickly in an emergency if needed. If it were even 20% cheaper for me, I'd dump the car... Operating the car probably costs me around $250 a month and I only use it once a week or so and never drive anywhere far.
Cars in Costa Rica cost about double what the same year and model car would cost in the USA, due to outrageous import taxes. (For the life of me I can't understand WHY Costa Rica is intent on charging all these high import taxes. It would benefit the entire population if they would lower the import fees significantly imho. But ...? And I often wonder WHERE all this import tax money goes! But that's not the subject of this thread... Though if anyone knows, pm me!)
So it's best if you can do without a car. There are also marchamo registration costs each year which is well over $100 a year even on an old car, much more on a newer car I believe. Then repairs, car insurance (I highly recommend getting extra insurance, not just the minimal insurance that is included with marchamo), gas, brakes, tires... it really costs a lot to have a car here; for many it is THE most expensive aspect of living in Costa Rica (unless you have to pay rent as well!).