This is just my opinion and I'd recommend a lot of more detailed research before you do anything - as I have no idea what your experience level is or what you mean by "budget" :)
Of course, there is no need to waste money - but I would be very wary of thinking in terms of it as a budget trip unless you are very experienced mountaineers.
As with any mountain, there are places that savings can be made - some of which have little impact on your safety e.g. quality of the accommodation when in the valley. One obvious way is to go with a group so that you don't have the expense of a guide for the full week (though with two of you, it may be worth looking into this, it might not be much less and it's much better.)
But many of them do have an impact on your safety because they involve less time and less flexibility.
Normally, you have a week for a Mont Blanc attempt, including acclimatisation, some practice with crampons & ice axe and a smaller, nearby summit. Cheaper variations can skimp some of this which is risky, or use a different guide to client ratio (this shouldn't be more than one guide to two clients for the summit attempt). Even quite small things can make a big difference - for instance, a cheaper operation won't have the time to advise you in detail on your kit and training.
At the moment, there has been very serious and dangerous rockfall on the easiest route, so many parties are going via the more technical 3 monts route, which requires more climbing skills - those extra days are vital here.
I would also always use local guides, as they are familiar with the conditions on the mountain at the time you are going.
There are plenty of excellent guides and companies in the area, talk to a few and see what you think.
We climbed it with Neil who I would recommend very highly - he's very experienced and a really nice guy.
It's an amazing experience - good luck!
Edited: 10:27 am, September 11, 2011