Don't use an agent it will cost you 10 times what it should.
Jump onto the Thai government website I'm sure you will find the relevant information there and download the paperwork. Email to the employer, I think that would be the easiest way if you are not in Thailand
I won't be here 20 years but a couple at least, I bought a cheap 4x4 250,000 cheaper than renting but still a decent outlay, so I agree 800,000 is basic