7-800 sounds about right (possibly up to a grand depending on labour). Some time back (actually nearly 20 years) I was looking at getting a box reco'd for a mini. There was one place charging approx a couple of hundred. Another place charged around double that, and there was a third place who wouldn't give a firm quote until they saw the condition of the current one - strictly price on application. I ended up doing mini boxes myself (and did a few for friends and stuff). The interesting thing was that even at trade price, i couldn't even source the parts for the total price the first place were quoting (and a lot wears out on mini boxes, you need to replace a hell of a lot of stuff each time as a minimum, and beyond that hte price can go up a hundred or two more depending upon the rest of the bits condition), Anyway - if you can't get the parts alone (at trade price) cheaper than a place is charging for a full reco, there's no way around it, they simply must be taking shortcuts, and not replacing everything.

I could tell the 'longer' version of this story, but the bottom line is you often get what you pay for with gearboxes.Some of the dearer places might still be dodgy, but you can bet your life that if the cost is too good to be true, then that's precisely what you're going to get stuck with.

It's probably also worth telling the reconditioner what the intended use of the gearbox is. It's a catch 22 - if you are honest, they might twist that and say 'no warranty if it is for non standard use'. But on the other hand, if you tell them the box is used for racing (just saying all this hypothetically) then some of the parts that might be ok for re-using in a daily driven standard car might be too far gone for racing apps.As an example - when the laygear bearings (sometimes called countershaft bearings) wear down, they allow the laygear to spin on an axis a little bit further from the gears on the input/mainshaft. As a result it starts t wear down the tips of each gear tooth. If you replace the bearings/and internal shaft, you put them back together as closely meshed as when new, but the wear on the teeth from the worn laygear allowing more clearance means they don't mesh across the full surface of each tooth like they did when new. For a non performance car, within reason, they will still last, and might have a whining noise that isn't too loud to tolerate. But for high output engines/competition use, this narrower contact pattern loads up each gear tooth in a smaller section and can lead to it failing.

I suppose the 'cheat' one can employ here (though it costs a lot up front of course) would be the idea of getting a later model gearbox from behind an L series engine and adapt it to an a series engine. Then even for performance use, if it wore down, and was rebuilt, it'd still have an extra 'safety margin' and there wouldn't be enough stress to damage the internals even under relatively hard use (for an A series at least)