Going to Bangkok is out of the question, to far, has anyone ever got a letter from the Imm office to tick this box.

If so, what do they require ?

How much does it cost ?

Could I just make a contract up with the friends I am staying with and they come with me if you need something from the landlord?

This below is form Thai Visa own website, with the link here.

The following are required to make the application :

1. Passport with valid Non-immigrant Visa. (Individuals with a Tourist Visa don’t qualify)
2. Present residence address certified by embassy or Immigration Bureau or work permit.
3. Medical certificate stating good health
Fee : 105 baht for cars and 55 baht for motorcycle. Applications for driving licenses for other forms of vehicle may not be grante

Mate, i got a letter from the local Amphur office,it just basically states your address,but as every one of my expats friends here has been asked for different things at our local licence office i would ask them first.

Yes no problem getting the letter only 100-200 baht if I remember correctly but you will need proof of address. Like a bank statement or rental agreement.

Just did it a few weeks ago, but here in Bangkok at Suksawat Immigration checkpoint. When submitting the documents, they gave me back most of the papers I had attached that prooved that I live where I stated to live. They only kept a few pages, not sure about which one. Took a week. 200 Baht.

Does it normally take a week or is it instant ?

Does the rental agreement have to be anything official as such ?

You get the proof of residency usually in a couple of hours. If you don't have any "official" document to prove your address go to one of those visa shops outside immigration I'm sure they will sort it out. You must have a non-imm visa though.