This is a good place for a beginner, as Ball Pythons are one of the better 'beginner' snakes. They're docile, easy to find captive bred specimens of, don't get overly large (usually 4 to 5 feet maximum in captivity), and aren't too terribly demanding on their needs. At a reptile show here in town, I paid $35 for my captive bred juvenile ball python. At reptile shops and pet stores, the average price I've seen for comparable size and normal coloring is $80. If you can visit a breeder directly, you'll be better off as you'll cut out the "middle man" cost, and will be able to get more background information on the individual you select.
Other good beginner snakes include the kingsnake and cornsnake species, which vary in maximum size depending on the particular species. Many of the king and corn snakes are also readily available in captive bred specimens. Rosy boas are reputed to be good beginner snakes, also being rather docile and not getting too large, but rosies are not as common to find captive bred. I've seen young cornsnakes for as little as $15 in reptile shops, though I don't think I've seen any rosy boas for less than $100.
For the beginner, I would strongly suggest staying away from imported or wild caught specimens, as WC specimens are often trickier to get acclimated to captivity, tend to be fussier eaters, and often tend to be less accepting of being handled.
If you can arrange it, try to find a breeder in your area and work out a deal where you can take your boyfriend over there and let him pick out his own pet snake from a "list" of available specimens in your price range. That way, he can have a better chance of finding an individual that he really likes and suits him.