When does the lid go back on the 'crazy' jar?

So, I went to extend my visa here in Nha Trang the other day. Last time I did this, the agent made a mess of it and when I got my passport back it was 2 weeks overdue with no extension, so I had to make a hurried exit to Hong Kong as I didn't need a visa for this destination. When I came back I flew through Ha Noi, then back down to Nha Trang...no problem...or so I would have thought...
Now that I try to extend my visa, I am told that it will cost $250USD for 3 months!
I've been to 6 different agents and all the prices have been between $220 and $250 - and the more I question it, the more frustrated and disturbed I get.
- Why is it so much more expensive for a Ha Noi visa extension? "Because we don't like Hanoi people"
- How much would it cost to renew if I was in Ha Noi right now?  "Only $35USD"
- How much would it cost if I had entered Vietnam from any OTHER border than Ha Noi? "Just $45USD"
- Who makes these ridiculous rules? "The govt"

Be warned travellers - do NOT enter Vietnam through Ha Noi unless you intend to stay in Ha Noi!

Someone should tell them the crazy jar is spilling all over the country and making a hell of a mess...