Agreed^
i`m a civil eng, but i`m an air conditioned office highways designer, not a wellies and boots kind civil eng you need.
Where are you based? Its only a small job but most contractors are looking for work and should take this up. At the end of the day its ordering a few gabions, digging a hole and placing them, you could always ask them to backfill behind the gabions to level out the garden, assuming some of it has gone missing down the stream.
Contractors i have worked with, mainly west midlands/ worcestershire way:
Hawk- might be a bit small for them
PM Harris (These dude's are cheap and this simple work would be up their alley- they also travel a fair bit- just spec stuff up front)
Owen Pell (hereford)
i`ll see if i can get soem more reputable names if you tell me where you are, through contacts at work or old uni mates in the industry across the country.
At the end of the day you need a contractor thats got equipment to take the gabions off the delivery vehicle, excavate a suitable opening (will prob be the same backacker/ digger).
For the contractor all he has to do is measure up the required no of gabions, order them in and set a delivery date. get the equipment over to you for delivery day and he'll possibliy just have two men there, a driver and a banksman/eng/supervisor.
i would set the gabions in the ground so they sit flush or below with your garden, you could then hide them by growing stuff on top, although it may go missing when it floods! You could maybe install your fence posts into you gabion too.
You will need a gabion matress as per the river erosion example in the link below, this should stop the gabion being undermined and putting you back at square 1.
http://www.weld-mesh.com/gabionstandarddesign.html
I`d give these guys a call and ask them to spec up a matress and wall solution which is suitable- they wont bite. Also ask if they have any contractors to recommend in your area.
you have about 10m of length, so 10 gabions, plus the matress of 10m length.
According to my 2010 spons estimating book (god i`m a geek), Maccaferri or or other equal gabions should be approx £220 for a 1m cube- inclusive of materials and labour for placing. That does not include excavation, mobilisation and profit for the contractor though.
£220x 10 for gabions
assume same for mattress, so £4,400 in materials.
Add on some delivery charges and cost for excavator and i`d say you are looking something like your 6.5k budget for your wall- maybe less if you can find a good contractor who's not trying to rip you off.
i`d question quotes over 7k, ask them for a bill of quantities if you think they are pulling a fast one and we can check their rates/ unit costs.
things to think about are delivery- can a large HGV get outside the house for delivering the gabions, and can you get access to the rear of the property for a backakter digger.
hope that helps and sorry i`m an office eng.