It is important to note what it included in the bathroom vanity; some bathroom vanities are no more than the wooden cupboards that go under the bathroom sink and the counter top and undermount bowl (sink bowl) then have to be purchased separately. It is a lot simpler and often cheaper to buy a vanity for the bathroom that comes with both these items.
A number of affordable options can be found at eBay. Some are used and others are new; the selection for sale on this site varies depending on what the individuals post for sale so you may want to bookmark the site and check from time to time to see what options are for sale here. Some items are shipped for free while others are not; with some items, you can return them and get a refund if you return the item within a specified time period and pay the return shipping costs. Other items can not be returned. It it noted on the site what the sale conditions are.
One online retailer that has a number of affordable options is modernbathroom.com. You should expect to pay in the range of $750 – $850, at least, for a new 42 inch bathroom vanity; a number of options in this price range are the Dalton 42″ Antique Bathroom Vanity, done in Cherry or Dark Cherry; it comes with an ivory marble counter and costs $800, and the Hartford 42″ Antique Bathroom Vanity, done in Antique White with an ivory marble counter top; this item costs $750. This site also offers free shipping of all purchases, which is another advantage, as many online retail sites require the customer to pay for shipping fees.
However, if you have a larger budget and want something truly classy, there are a number of 42″ vanity sets that cost a bit over $1,000 that would look great in any bathroom. The Accara 42″ Bathroom Vanity selling at the above mentioned online retail site comes with six drawers, a cupboard, and glass counter. There are a number of classy looking Hana bathroom vanities available here as well, in a variety of colors, for $1,200. These include drawers, shelf space, and a large mirror as well.