WobblyJohn is correct - the current 9/10/11 body is compatible with the 8s sprockets but a 2mm spacer behind the biggest sprocket, plus a small reset of the limit screws is required.
It is also important to point out that the tightening torque of the lockring needs to be observed as the older sprockets use a shallower spline and no alloy carrier on the lower sprockets (which in general are transmitting more torque to the cassette body) so the potential for the sprockets to either mark the cassette body, or in extreme cases, to damage the cassette body over time so badly that they will actually spin round it (you have to try pretty hard to let it go this far but I have seen it) ... is greater than with the more recent, deep-splined 9/10/11s sprockets.
This is because the original 8s bodies were steel, whereas more recently alloy has been used for the splined part (and most recently, since 2006, for the whole cassette body).
On the wheelbuilding question, to a certain extent you get, provided the wheelbuilder is honest, what you pay for. It takes me around 40 min to 1 hour to build a "standard" wheel - i.e. one with conventional spoke pattern, spokes and nipples - and I charge around £40-50 + spokes. I could do it in half that time (and therefore at half the labour cost) but wheel trueness and equality of spoke tensions would not be as accurate. Also, you are paying for the time taken to sort out exactly the right product for what you want to use it for and the 30 plus years of experience that sit behind that. We give full data on every wheel we build, too - actual spoke tensions in the form of a radial tension graph, the actual rim-run outs radially and axially and the accuracy of the dish & offset. Others may do it cheaper and just as well, of course - how we choose to price all these little slices of our finite lives we sell off to others is a personal decision!
Factory built wheels may and may not be done entirely by machine, partly by machine & finished by hand, or completely by hand. They build in large numbers and to one specification which is a one-size-fits-all approach which rarely makes the most of the available bank of components as the manufacturer has to think of 60kg racing snakes in the same mental breath as 100kg commuters - all the recommendations under the sun about rider weights won't stop a vendor selling the wrong wheelset to the customer, nor will they prevent a determined customer from trying to out-bling his mates and in any case, just the weight of the customer has relatively little to do with whether the wheel is a sensible compromise for that individual - wheel makers know this so are pretty conservative, in general. This allows them to be very aggressive on prce against a more artisinal "right product for you" approach.
There is a "third way" to the tubular x likelihood of puncture question and that is to run something like Tufo tubulars with sealant - that will work for cuts up to 3mm or so long and is reliable. We do it on our racing tandem as a front flat on a tandem is pretty scary and a front flat on a clincher on a tandem is pretty much uncontrollable, so Tufos and sealant work well in that application. +30g in each wheel for the sealant is no big deal unless you are racing and even then *to finish 1st, you 1st have to finish ...". We race. We (used to, back in the day) even win, sometimes ...
I'd expect to pay half that for Mavic Open Sport and stainless double butted.
