Although most projects are based on a flat rate, custom work can rarely be predefined price wise. Having said that, a $100+ for a personal and unique artwork on a t-shirt or a leather jacket is a standard base price to start with.
Prints, posters, cards and what have you all have their reproduction rights evaluated prior as well, mostly dependent on territory, quantity of prints, size and duration of campaign. Custom works on such things as car and bike murals also fall into the realm, and $500 to $2200 for helmets vs $1,500 to $10,000 + for cars are standard pricing based on design, material needed, time frame, client alternation during and after project etc.
Again nothing is set in stone and these are only basic guide yet they are in-line with current market trend in the customizing field. Our work is second to none and referrals are handily available.