I personally think eBay is always worth a shot, as long as anyone who gives it a go knows, understands, and can accomodate some of the risks and requirements that are involved. This is especially true when starting out small, because while an established business seller might be able to absorb a $100 loss on a product (be it lost in transit, damaged, faulty or effectively stolen by a fradulent buyer), it can be a bit more devastating for a smaller seller. And I'm not saying this to scare you away, I'm saying it so that you can formulate a business plan, and other strategies, to cope with something like that if it ever happens - it may never happen, but knowing that it could is something that can help ensure you can more easily recover if it does. 

Re: opening a store, it's probably not worth it until the $19.95 monthly fee (for a basic store) will cost less than what you'd pay without a store, but that's reliant on quite a number of factors, some of which don't have any actual monetary value (eg Store categories, helpful when you have a variety of stock listed which can cross-promote one another), while others do (eg difference in FVF is usually minor, but you do get access to more features, including longer listing durations).