@SharpyClio Having done a bit of 'detailing' on the side now, im in a position to offer some advice.
I started off doing the same thing as you, but for friends not a bodyshop. I also used to spend nigh on 6 hours, busting my arse, and usually charged a flat rate of £100 too.
But, as I got busier and busier, working almost every day off, I just thought 'f**k this, im ramping my prices up'. I now charge £20/hour and im still bloody busy. Like you, im not there to earn mega bucks. I just want something to do on my days off and usually the money goes towards my track time (now its the house). I also really enjoy the challenge of it.
I guess what im trying to get at is - Only
you can decide if its worth it. If youre getting £100 for some spare time and thats fine by you, crack on! I weighed up my options and what I could earn at work and decided on that price. I also did a basic spreadsheet with the costs of materials and that helped my decision making.
Good luck! Car looks great btw