I am interested in purchasing a treadmill brand that has good after sales service in Thailand. Does anyone have firsthand experience with brands available here? 

There is a guy on the pattaya forum one more chang who seems to have his own treadmil you should ask him. But you have to understand of all the cardio machines the treadmill is one of the most expensive and most prone to damage.  I got a rowing machine Concept 2 model D and a Sole E55 elliptical. I never had to do anything with the rowing machine.. its bulletproof. With the elliptical i got good after service (something was wrong they came to fix it) 

 

This came from the shop i bought it from (through home pro website) Seemed all good. But only the future can tell. I hope it helps.

Sole F63 , Horizon advanture 2+ or BH fitness F1 are the model that popular for home use treadmills in Thailand. Pricing around 30,000-50,000 ,  not cheap but it's far better than a lot of chinese made treadmills.

If your jogging is not more than 45 min per day, running at the park is better. Treadmill take a lot of space, expensive and hard to maintainance.