The Educational Visa (short ED visa) is the easiest visa to obtain, that permits you to stay long term in Thailand.
The ED Visa is based on a school that sponsors you. For Example, Universities, Language Schools or even Muay Thai Gyms (Thai Boxing).
The costs for the visa depend on the school and on how long the visa lasts until it expires. But you can expect around 30,000 baht (860USD) for 6 months or 50,000 baht (1,400USD) for 12 months. But I also saw it cheaper at other places as well.
You pick a school, preferably a Thai Learning School or if you like Muay Thai then a Muay Thai Gym that offers ED Visas. They will ask you for some copies of your passport, some passport photos, proof of your hotel address and a few photos from a lesson you take and a few signatures. A week or two later, the school takes you to immigration, where you sign a form and give them your passport. Another two weeks later, they send the passport to your school with the visa stamp in it, and you can go pick it up. This whole process takes about a month, So make sure you still have a month left on your visa when you apply for your ED visa.
The stamp you got in your passport now is valid for 3 months, so every 3 months you have to go to the specific immigration office you applied at and get a stamp for another 3 months. You can only go to the immigration office to applied at, so if you apply in Phuket, you can't go to the one in Chiang Mai, you have to fly back to Phuket after 3 months to get it. So for a 12-month visa you have to go on day 0, month 3, month 6 and month 9 to get stamps.
In Theory yes, but practically you don't have to, it's enough to show up every 3 months, study a couple of hours and get some pictures taken and go to immigration to get a stamp for another 3 months.
With an Educational Visa you don't have to do visa runs every few months, and you can apply for a Thai bank account and Thai driver's license.