First things first. When I'm talking about budgeting I mean purchases made on the show floor, or paying at the table for autographs on the auto hall or artist alley.
Most celebs on the floor or doing table signing in the auto hall usually fall in the $60 flat, $80 premium range. This was based on what I saw last year.
Comic book writers and artists in artist alley typically go from $10 to $50+ depending on how big of a name they are. Ex: Kevin Eastman carried $60 price tag the two times I got things signed by him. He also required you to get spot holder in the morning so you could get a spot on the line later that day for his booth in artist alley.
Typically what I do is I plan out what I want to accomplish each day ( I go multiple days to spread the cost). Then I plan out what it would cost each day. I usually add $20 to each price in case prices were increased from last year. I also add and extra $50-100 dollars to the days total in case something catches my eye, the extra cash I added helps cover that cost. I only carry that days cash total, and leave the rest in an envelope at home. When I get home, I clear out my back pack, reload my wallet with the next days cash.
When it comes to travel and lunch I put that on my card. I take the LIRR or the 7 train, so cost for tickets are paid for either via the LIRR app or my OMNI card. Lunch I hit the food trucks outside the Javits, I keep myself on a budget for $30-35. This usually covers a meal plus drink, sometimes I forgoe the drink because I carry 1-2 refillable water bottles.
Large merch purchases $!00+ plus are put on my card, and small merch purchases <$100 I pay with the extra cash for that day. I limit myself to 2 large purchases for the duration of the con and 4 small purchases for the duration of the con. Sometimes I hit all 6 purchases, but most of the time I'm taking home the extra cash and keeping in my wallet in case I need it.