If you are developing your own platform to sell from you should be looking at how you are going to target your market (how you are going to draw targeted traffic to your site)
Of course with your own platform you won't be subjected to listing and final success fees and that will always be an advantage, but you will of course have the general cost of your site to cover and the marketing of that site which can be an extreme expense.
Why not take a look at your business model inside out to get some ideas. It seems that you don't really care about what you sell, but being really successful is all about knowing your market, and knowing your market includes not only knowing your product, but also knowing the type of people who will be your primary demographic.
If you don't know who to market your products to, then the chances are that you marketing dollars won't be delivering you any real value at all.
Why not take a look around town and some businesses, see if you find something that you could get interested in. Approach the business owner with a joint venture plan.
You will market their stock on your site for free, in return they provide you a reduced price for margin and process your orders to ship direct to your customers upon sale.
Present the proposal correctly and it will be an easy decision for the business owner to make. Marketing is key to any business, and they will always be looking at effective marketing avenues that offer them the biggest bang for their buck, and it doesn't get much better value for a business owner when some free marketing comes their way!
Of course this would only work if the business didn't have their own site already, but the fact is that there is still more businesses offline than are actually online, so there is opportunities for joint ventures available everywhere.
If you're smart you will your site in their shop, after all it is now an extra added convenience for their customers to be able to shop 24/7.
It basically solves the problem you have of trying to establish a market, it only leaves you with the issue of marketing to targeted traffic.
Why stop at one store, set your site up to sell for other businesses in your area, create your very own online department store!
It's true what they say, no one ever gets big by thinking small : )