There's the supplies, cooker of course, tables, chairs, knives, cutting boards, sinks, tents, etc.
Average sanctioned competition entry fee for a smaller competition, say KCBS, would be around $250, not including any entry fees for peoples choice or ancillaries. Meat, spices/rubs, injections, foils, etc. For very short trips, say under 2 hours each way, we'll spend $700 to $800 total. That's KCBS, FBA, etc. MBN, so far I haven't spent less than $1,200, but I hope to do this very thing this year at a close one where I have no travel costs (well, $10 in RV gas) and entering only ribs and pork shoulder, no ancillaries, and hopefully we'll cut it to about $900+-.