purchasing a vehicle with BitCoin and Challenge budget

GameboyRMH said:

 turning vast amounts of energy into waste heat.

This is a huge problem I have with cryptocurrencies.  

I've thought about only mining during the winter where waste heat will help keep my house warm, but now my GPU is so out of date its just easier to buy them.

If only I could. Just one of the quite literally dozens of mistakes I've made that have cost me large streams of money in my life. 

Anyone is free to go look for the remnants, they went in the trash around April of 2012 in Lincoln, CA. I'm not sure where the dump is though. At that time, bitcoin's were 100-200 dollars, and data recovery(clean room hard drive rebuilding) was running around $1500/GB. Not worth it then on a 500GB or 1TB disc. 

As has been typical in my life, I recommended everyone I knew buy some and hold onto them, and as usual everyone ignored me. $1300 would have been a win, $5000 ridiculous, currently at $8k just berkeleying shoot me. Just like they ignored me when Google went public, and with Apple, and with Facebook(which was smart to ignore me at the time because of how Zuck shorted the IPO).

If I had money to follow to my own advice I'd be set. If people would ever actually fixing listen to me for a change, they'd be set. Unfortunately, I'm perpetually poor, and people are perpetually stupid. (Last paragraph not aimed at anyone here, more describing everyone I know locally in real life)

answer to original question is pretty simple.  conversion rate at time of purchasing parts/car/etc. 

If you buy an engine for 1/2 a bitcoin on October 1st.... and that exchanges to $500 USD at that time, that's how much of your budget you used.  

If it appraises higher 3 months later it's irrelevant.  If you purchased the bitcoin for $100 US earlier, that's also irrelevant.  

I could've bought Ford stock at $5/share a few years ago.  This year I decide to do the Challenge.  I sell my Ford stock at $12/share and go buy parts and a beater car.  The # of shares of F stock used is irrelevant, as was my cost basis in it.  All that matters is how many dollars worth were used to acquire/build racecar.