Help with patio enclosure pricing

Hi - we're in the process of getting some quotes from patio enclosure companies, you know, the ones that do 'queensland rooms' and the like. Unfortunately none will give us a straight answer when it comes to price, they're much like car dealers and rather than give quotes, they ask "how much do you expect to pay?".
I was hoping someone could give me a little feedback on the sort of price we're getting quoted, as after the high-pressure sales we've been inflicted with, I'm feeling a bit lost!
Ok, we just want an embarassingly small enclosure... here is a rough diagram:
http://i6.photobucket.com/albums/y20...nddh/patio.jpg
This is the front entrance area of our brick veneer house. The solid line around the edge is the eave/roofline, the black dotted line is the actual house, and the red line is the enclosure we want. The black square to the right is a brick pillar. The patio area is under the house roofline, and is concrete slab.
So, we just want two 'walls' added, then we will remove the front door 'wall' on the left (which consists of a door and a floor-ceiling glass pane). This will result in a whole new small room (~3.2mx1.6m) that we can use for a very compact office. I hope this all makes sense!

The quotes we've got are for the supply/fit of the two 'walls', one of which is basically just a custom fit sliding glass door, the other is a frame containing a 1200mm window & textured fibrecement type panels.
No demo of original door, painting, flooring etc is included.
Prices are around $3,700.

Would really appreciate any feedback on this! Seems like such a small job to get done, I feel almost silly asking about it....

(and yes, our house is so compact this would make a huge difference! :o)

BLT,

I would suggest that you ask your tradie as to why he won't give you a straight answer. Most trsdeis I know will happily supply a written quote. Its a matter of asking for what you want. If they still continue this line then seek another quote from some one else.