If you only have a few items, a store may not be all that viable unless you can turnover enough to make the $50 fee worthwhile.
The main advantage of having a store for you would be being able to create one Buy It Now listing with multiple quantities of the same item available, and that the listing could remain live for as long as you have stock available rather than just 10 days. The option to list multiple quantities as a BIN listing (10 day duration) will become available if you reach Power Seller status, so if you sell successfully enough (100 transactions and US$3000 worth, in any 12 month period), you'll be able to do that instead of listing them individually.
Unless you have other selling restrictions imposed, you can list and sell more than 30 items a month, it's just that the first 30 don't attract a listing fee (which are 50c for up to $19.99, $1.50 for $20-$99.99 and $3 for $100+).
If you have a store, the listing fee will drop to 20c per listing, regardless of quantity available, but if you use a multiple quantity listing as a Power Seller without a store, it will be the listing fee X quantity (say the price is set at $22 and you have 10 available, your listing fee would be 10 x $1.50 = $15.00). The final value fee would also drop from 7.9% to 7% if you had a store.
So, obviously there would be a point where having the store would be more economical, but it really depends on whether you do or don't achieve Power Seller status, how much stock you have, and how often it would sell.
