I'm going to do my best to do a cost break down! I've also added links when I could to give more info.
Motorcycle without a title to build my working prototype cost me $100.
2nd motorcycle with a title and lots of good gas engine parts to sell cost $250.
Golf Cart motor from an Ez-Go cost me $200 but if I bought more $150 each should be possible, that $200 included a main solenoid shut off if I remember correctly, that part would have otherwise cost $35.
Magura 0-5K ohm electronic twist throttle I found one for around $50 with shipping.
Used
Alltrax 4834 speed controller $170 with shipping, rough specs are 24-48v 300amp peek 275amp 2 minutes, 125amps for one hour.
Battery cables were $8 to $15 each for the lead acid batteries, 6 batteries so 7 cables total, it took three long $15 cables and 4 short cables so round it up to $80 for battery cables for the golf cart batteries, I could have saved money by buying cable ends, bulk cable and crimping them all together my self but I wanted to use off the shelf parts as much as I could.
I've tired two sets of batteries now, the old set I paid $20 each for 6v golf cart batteries that are now 8 years old, the other set belong to my parents and they paid $97 each, those new batteries are what I used to get my 40mph top speed test with, using 6 of those batteries, after tax the lead acid battery cost was around $610, the used set of batteries cost $120 total and worked pretty well for their age!
When I go to lithium batteries I figure my full lithium set up will cost $2616 and it could be lower if I can get someone else close by to order with me ($5000 to get a bulk discount), but that price is
16 100amp hour lithium cells, BMS, charger and gauge that all connect and talk to each other
My current battery charger for lead acid is something that I had left over, it's
a 4 bank (4 12v sets) NoCo brand charger designed for trolling motors on fishing boats, I paid around $300 for it, nice for lead acid batteries but it charges kind of slow.
Steel to make a battery box cost about $45 for the sheets of steel plate cut to my specs, I then welded them together.
Each motorcycle has about $15 in raw aluminum that was then CNC machined and my current adapter shafts are $9 chunks of P20 tool steel that were then CNC machined, that tool steel was over kill so the cost would come way down on the metal and my brother thought it would cost about $300 to machine everything but I'm still waiting for all my drawings to come back to me for a true bid.
Ball bearings, I used two
6005-2RS sealed ball bearings that I paid $3.38 each.
I'm sure that there are a few misc parts that I've forgotten about and if I remember them I'll add them in, but so far this is what I have bought and how much I spent! let me note that I have not yet bought a DC to DC converter to run the lights, that will be an added cost unless I opt for a 12v aux battery and a charger to charge it, I also haven't subtracted the money that I could make from selling parts or selling scrap that I remove from the motorcycle.
Total spent to make my 40mph test run came out to $1577, using the frame without a title and using new batteries, after making that test run I had some machine shop work done on the motor to fix the commutator and that cost $38, the new lead batteries are not mine so that cuts my out of pocket costs by $490 but I'm sure that it would also have cut my top speed by a bit if I had used old batteries.