Agent spinning me a yarn?

So just to wrap up on this and provide closure, I ended up going the agent route as it is too inconvenient for me to leave the country right now and I wanted as close to 100% guarantee that I will get this visa without issue.  I went to see 2 different agents, Manereet and OneStop and the user experience is quite different between them.

Manereet.  Cost of 3 month Non-o + 12 month extension = 30,000.  Operates a bit differently to how I would expect an agent to work as they give you a list of things to do yourself such as get 6 passport photos (not included in the 30,000 cost and have to be obtained from another shop) and give a slip of paper to pass to the bank, again to do by yourself.  They do not seem to do much (anything) in the way of "hand holding" nor explain much (anything) about the process or where the passport will be sent to (just they need to keep for 1 month), hands you a couple of slips of paper and sends you on your way to do the initial busy work.  Also wanted "ATM Card" for reasons they didn't explain which I found very strange as the ATM card doesn't even have my name on it, and the only useful info on there is the card number, expiry and CVC code. 

OneStop.  Cost of 3 month Non-O + 12 month extension = 29,000.  Operates like I'd expect an agent to operate, gives full advice, takes photos and printouts in shop, accompanies you to the bank to explain what is needed to the bank clerk and then meets at immigration for another photo taken by immigration to get the 3 month visa.   So this is the one I used as they didn't send me on my way with a couple of bits of paper to do the busy work, they actually helped.   They did not want or need my ATM card for anything.   

Inflation seems to be quite high in the agent world as both quoted 3000+ more than when I went to see them last month.   For time reasons I didn't try any of the other agents to see if cheaper options available.   Using your own 800K in the bank seems to have no impact on the cost of visa via an agent, but I used my own anyway so that I can DIY next year if I want to or I can always not worry about keeping the account 800K+ and pay 15K next year to use agent for 12 month extension.   If I'd had the foresight to put the money in the bank a week or two earlier I would have saved myself 20,000+.   Lesson learned.

One other clarification point is that it seems the Non-O visa has to be applied 20-21 days in advance of visa exempt expiry so I presume the 15 days mentioned earlier in this thread is 15 business days.