From what I understand, bronze tools and weapons were valuable and somewhat rare items that not everybody could afford. Were stone tools ever completely replaced by bronze tools or did this only happen with the advent of iron?
Stone tools were never completely abandoned. Hammer stones, grinding stones, pounding stones, anvil stones, polishing stones etc. have their uses in many industries as well, such as the collecting of metal ores or smithing. Flint has continuously been used as a cheap material as well, in areas where it locally occurs, such as in threshing sledges. However, the craft of flintworking in Europe had its peak during the Early and Middle Bronze Age, up to around the 18th century BC. Some later pieces up to the Iron Age prove that craftsmanship (which is definitely a necessity when creating the nice pieces we see) was continuously kept alive to some degree, but absolute masterpieces like the Type IV daggers or the flint copies of metal swords were not matched.
You should not necessarily think of these flint artefacts as simply 'fake' or 'cheap' replacements of metal originals, as the amount of skill required in making them is enormous, and the flint nodules of sufficient quality and size to make these objects must have been mined as well. The most sophisticated pieces are also way too brittle to be used functionally in anything but ritual context, and should in my opinion be seen as mostly show-off status objects with their own specific function in society, not necessarily the same that their metal contemporaries had. Rather, we see a 'show-off' tradition in flintworking also in the preceding Neolithic. The long daggers from this period always consistently have a piece of cortex (the natural 'outside' or 'shell' of the flint nodule) on the butt end, showing that the flintknapper made the dagger as big as he could without errors that would have required a shortening of the piece. Thus, these objects can be seen as conscious displays of the flint-knappers skill. In this sense, the flint sword represents an 'otherworldy' artefact that could not simply be reproduced by anyone.
More mundane uses of flint tools, like hide scapers or arrowheads, are superseded by metal versions during the Late Bronze Age, in the period from 1200-500 BC.
The standard book on this is Eriksen's Lithic technology in metal-using societies.
Obsidian is still used for blades. But each piece is handmade, so it's pretty expensive.
One vendor is here:
http://www.finescience.com/Special-Pages/Products.aspx?ProductId=296&CategoryId=56