Hello, just adding my 2 cents, =P hope it helps
to be honest I really don't think that you can get a drumset piece by piece. seems really hard to find. rarely find people selling just the bass drum to you. =P what they said above about practicing on pillows and stuff really does help. If you are really hard pressed for money now, don't rush into buying a drum set. If you get a really cheap one to tide you over now you might regret it later. you could get a practice pad and some sticks. That would simulate hitting a real drum more and let me assure you that most drummers with complete drumkits will also have a practice pad. Its quite an important piece of equipment for drummers.
There are a few things i feel that every drummer "should" have "should" meaning "if money permits". every drummer should have his own sticks(duh) drum key, snare, bass pedal and maybe cymbals. lol. the bass pedal i feel is one of the most important, as you learn how to play the drums, you get used to a certain setting you like of the pedal, and when you play outside and stuff you should bring your pedal, you'll be suprised how badly you will play on a pedal you are not accustommed to. of course you could always adjust the pedal given but you might not be able to depending on the circumstance.
As for the bass however, i really have no idea what you can do with it. I have wanted to get one of the practice pads with a pedal attached, but the stores here usually sell those in a set... if you know what i mean essentially its a practice pad that allows a drum pedal to be attached. I guess theoretically you could buy a drum pad and try to make a stand or something. look here for a better idea.
http://www.vintagedrum.com/item/Gibraltar-10-Bass-Drum-Practice-Pad-DY-PA757BDP
or just go to your friends' place or church and whack every weekend.
Sorry for the long post. Just want to help. If you want to know more you can pm me. Not that i'm an expert, just trying to help. Oh and one more important thing, even though it sounds stupid, it helps if you try to make the sound of the drum with your mouth. I mean, without even hitting anything, mouth out what you are going to play, like "papapapa, boom boom boom, booooom booooom booooom, chang!!!!" it may sound dumb, but thats what my drum teacher used to get me to do for fills and stuff.. it really does help IMHO, as i think it helps you know what you are going to hit next. I've read posts from other drummers in other forums that say their drum teachers made them do that for months before they touched the drum lol. Hope i at least made some sense. All the best