The prices in price guides are obsolete the day before the guide is printed. However, the guides are quite useful for other information, as in name and genre of set, number in set, pictures (check the gallery on this forum for GREAT pictures - thanks Dan), variations, short prints, etc. Many different guides have been printed that have this information. There are several threads on this forum with this information, if you will do a search.
But back on prices:
If you just inherited a group of older cards, try to determine what they are (members here are great with help), and then search Ebay for completed auctions. If by some quirk of fate you found some really rare stuff that is not on Ebay, post here for assistance.
If you are wanting to start collecting, again, check completed auctions on Ebay.
Unfortunately, Ebay is pretty much THE price guide now.
My opinion, others will differ.