Due to HH Immigration being greedy bastards and totally unhelpful it seems I will need to do a visa run around 17th/18th October to get a 15 day extension or else I'm in the sh*t. I have never had to do this before so am pretty naïve as to where to go and what the process is.
Can anyone offer me some sound advice on this? Also, if anyone is aware of any laid on trips to do this, that would be even better.
Never done it myself, but a friend used a place across from the railway station. He basically said they did what it says on the tin - no frills, but he got what he paid for. It mentiond visa runs on the shop front to the left of the eating places.
The easiest thing is to drive to Ranong (400Kms south) then pass through Thai immigration then get on a boat for 25 minutes (400baht return trip, cheaper if you don't mind sharing) to Myanmar. In Myanmar you need to pay 10 USD in cash (a nice crispy note) they will stamp your passport in and out at the same time then back on the boat and arrive in Thailand at immigration and you will get 15 days. This border is only open during daylight hours I believe, you wouldn't want to go on a longtail in the dark anyway.
You can do the same thing at Sadao/Malaysia but you don't need the boat or the 10 USD but it's about 800Kms south. This border is closed from 11pm to 5am.
If you don't have a car...
As BB points out there are some places round town that offer 'Visa-runs' presumably to Ranong but then you are at the mercy of your mini-van 'driver'.
You could fly out of Hua Hin on Berjaya Air to Kuala Lumpur but their scheduling means you have to stay in KL for at least one night and possibly two, about 9000 baht return, not including hotel costs. I'm not sure if you get 15 or 30 days entering from Malaysia by air rather than ground.
You could get the airport bus (safer than a mini-van by all accounts) from Hua Hin (300 baht each way) and fly out of Bangkok to Vietnam or other non-bordering countries, its possible to get an early flight out and a later flight back to Ho-Chi-Minh on the same day for around 5-6000baht. In this case you will get a 30 day stay. You could also do this if you have a car and just park in the airport.