I chatted this morning with another coworker, Jane, who has crocheted for decades, so she knows a lot about things like cost of materials, time and effort, and quality of work. She said my quality is very high, since the stitches are even and consistent both front and back. She even said I should enter a piece for judgment at a craft fair! Based on her experience, Jane said for a queen-size afghan (which is what my coworker Thomas wants) I should charge at least $300. I searched Etsy for "queen size crochet blanket" and the AVERAGE results I saw which weren't just people clearing out their attics or doing something very elaborate ranged from $200-$400 depending on the pattern. So based on all that input, I think that's a fair price.
I told Thomas the going rate on Etsy, and based on the retail cost of materials for my mum's afghan, about $60-$75 would be materials. I told him I will look up patterns that are within my skillset and send him some examples to pick from. Then we can discuss how many/which colors he prefers, and ultimately settle on a price. I told him, minimally, I would want cost of materials up front, just in case something unexpected happens and he changes his mind or cannot pay me the rest. He said he would be comfortable paying me half up front and the other half upon completion. I let him know I will be finishing my mum's and boyfriend's birthday afghans first, so I can probably start his sometime next month.
I am getting pretty excited about this prospect of being commissioned for my new hobby. I will probably search for some one-piece afghan patterns this evening, in addition to the ones I already have my photos of, and send those along for him to mull over.