At one point, when I thought I had some money to spend, I made a spreadsheet comparing various kinds of batteries in terms of cost, range on my bike, and the most useful metric, $/Wh. You can always take smaller packs and put them together into a large battery pack, so it's not the cost that matters, but how much you're paying per unit of energy. It's also useful for comparing between different types of batteries. You can look at this spreadsheet here, or like almost all the document for this project, it's in the Google Drive folder linked in the sidebar.
Lead acid batteries, as I said above, are pretty poor batteries in almost every way, except that they are incredibly cheap. I won't get into the other kinds of lead acid batteries, but the most common sizes of sealed lead acid batteries are around $0.10/Wh.
Most home-built electric vehicles built now use Prismatic Lithium Ion cells, because they are very large (ranging in size from paperbacks to telephone books) and thus fewer are needed, making them easier to work with. They usually use Lithium Iron Phosphate (LiFePo4) based chemistries, because they are extremely stable and can't catch on fire unlike the other Li-on chemistries. The gold standard right now are the CALB CA cells, which are around $0.40/Wh.
NCR18650B cells, which cost $0.49/Wh in medium volumes. Some cylindrical cells, such as the very high quality LiFePo4 18650 cells made by A123, cost upwards of $2/Wh.
|The NCR18650Bs I use in my flashlights|
UranusFire). You can buy old laptop batteries off of eBay for around $10 a piece, which if you assume you will get an average of 4 working cells at 2Ah a piece, is $0.34/Wh, about the same price as RC LiPo.
|Cracking open a Toshiba laptop battery.|
|Six Sanyo Cells|
|Most of my laptop salvaged batteries|