Accounting Experts come in! LIFO, FIFO, AVERAGE, CASH BASIS?! Need Advice.
 

I need a local card shop owner or an accounting expert's help. I'm computing my profit/loss statement on a weekly basis now, as I am seriously considering going full time on ebay and online card sales within the short term. I'm having problems with inventory management and costing out a box of cards.

Example. I bought a box of 2011/12 Panini Past & Present Basketball for $110.00 shipped. I spent 3 weeks selling all the cards inside the box, due to other time constraints, and I use cash accounting right now to cost out expenses and I'm running into some constrictions with it that I don't like. Here is the problem:

Week 1. Buy the box, open it, sort it. Expense = $110.00, very big loss that week.
Week 2. Sell most of the hits and inserts, Very big profit of around $80.00 as the box of Past & Present was already expensed out.
Week 3. Gain of $30.00 selling the rest of the inventory.

I broke even on the box, pretty much. However, I want to avoid expensing out the $110.00 the first week. I also don't have a set time frame in which I usually sell boxes.

LIFO and FIFO wouldn't really work, as I don't know in which order I received the cards.
Average wouldn't really work, take $110.00 and divide it into 200-300 cards and that would be a huge gain all the time, and if I do go public, a huge tax bite at the end of the year.
Cash has worked up to now, but I don't know of another alternative.

Could anyone give me pointers? Am I doing anything wrong?

bumping...because I want some similar advice.

When you buy the box your would:

Debit - Inventory $110
Credit - Cash $110

Sell cards:

Debit - Cogs $xxx (cost of cards sold)
Credit - Inventory $xxx (cost of cards sold)

Debit - Cash $xxx (selling price)
Credit - Sales $xxx (selling price)

Your margin will be the mark-up (difference between the cost and selling price). You need to properly match your sales and cogs within the same month. You would never do weekly books, so monthly is fine.