A good 802.11g Wi-Fi access point can be had for between $50 and $100. If you are willing to settle for 802.11b, you can get one for well under $50. By contrast, an elegant 802.11g unit, the Apple Extreme Base Station, costs about $250 ($200 if you take the model without the external antenna port). Although industrial-strength commercial units can cost a good bit more, the point is that these are not hugely expensive pieces of equipment.
You'll pay more for 802.11g equipment than for 802.11b equipment because 802.11g is newer and faster. This is a choice with obvious trade-offs that you'll have to make, but at this point the balance has pretty much tilted toward 802.11g because the pricing has come down so much.
Likewise, the Apple Extreme Base Station costs a little more than equipment manufactured by a vendor that is not Applebut then again, it looks so cool. You'll have to decide how much the cool factor matters to you.
Even if you buy your access point in the real world of bricks and mortar, it makes sense to at least comparison shop online.
Be sure to buy the equipment you need. You can buy a wireless access point that also includes the functionality of a router (for example, the D-Link DI-624). Some wireless access points do not provide the router functionality, so if you already have a router you can buy one of the wireless access points that does not include a router (for example, the Linksys WAP 54G).
I'm a firm believer in buying equipment from quality vendors that stand behind their products. Quality manufacturers of Wi-Fi access points include