I'd like to try doing commissions in the new sketch-y style I've been using recently. If things progress, I'll make a proper submission for the info which will be simpler to read.
BASE PRICE (standard sketch): Feral - £8 GBP Anthro - £10 GBP Prices may be higher depending on complexity of character. Things such as wings may add a little, for example. Example: http://i.imgur.com/skzmBKu.png
ADD FLAT COLOUR: £5 GBP A large complexity of colours may increase this, but you probably don't need to worry about it. Example: http://i.imgur.com/OdraTTq.png
ADD SHADING: £6 GBP If the character is complex enough to increase the base price, the shading will likely be a little higher too. Example: http://i.imgur.com/yme5mqT.png
EXTRA CHARACTERS: Each will be +75% to the price. (the most "expensive" character will be full price, any others will be discounted)
That's about it for the main details, but just as I've been writing this I figured I could probably do head-shots/icons too. Icons would be £8 GBP for flat colour, or £10 GBP for shaded.
A final note about payment/currencies: As opposed to what I did last time (convert the price from GBP to the commissioners desired currency before sending the invoice), I think I will just send the invoices in GBP since, as far as I know, Paypal just converts it from your primary currency automatically. This should be a lot simpler since I don't have to confirm with people what currency they want to use. If there's some important details about this that I'm missing, let me know!