Aw man that is right up my alley! Build it!! Build an ebike!
I slapped one together in my college dorm room years ago and it was the funnest thing ever. I bought the motor/hub used, got a free junk bike frame and went nuts.
Lead acid isn't the worst way to go, mine was setup at 36 volts and it was heavy, probably a 60 pound bike, but still quick I could go 17 MPH on it no problem and hold 15 MPH up hills.
I miss that old bike, it was really handy I rode it all over campus and in town. A little small but that used motor/hub I bought had a fixed rim so no option to add a larger tire to get it on a bigger bike frame, I wish I would have had a 26 inch tire!
You said you found the motor at walmart? In store or online? I assume yours is a brushless motor also? Did it come with a controller? Did it come with a freewheel hub and gears?
I do have two spare brushless motor controllers lying around if you decide to pursue the project, although you can find them cheap anywhere nowadays. You also need a throttle/pot.
One option you could explore would be to build a battery backpack. A little clunky perhaps but then you can save a lot of effort on figuring out how to mount batteries on your bike, and upgrade to lithium someday. The pictures above are of my second electric bike, my first one the batteries where in a backpack with a quick connect power cord.
I used 12 ah batteries in the project shown above, I could go between 7 and 14 miles depending on how I drove it. If you don't need to go far 10ah batteries may suffice which saves some weight and sometimes you can scavenge those cheap as they show up in used computer battery backup systems and stuff.
Now you got me all excited about ebikes, I wish I had more time and money!
This is an old Suzuki motorcycle frame I hope to put a large brushless motor in someday: