I sell a lot on ebay in fact it is part of my business however I don't sell clothes more collectables vintage antiques etc
the lowest reserve you can set is £50 and it costs, everyone can list 20 items a month free whatever starting price is I suggest you start at the lowest possible price you would accept
for personal / private sellers the costs are ebay 10% commission on item and postage charge and paypal take 3.4% plus 20p per transaction as crazy said sometimes they do a £1 deal
so if item sells for £10 with £ 3 postage, ebay takes £1,30 and paypal takes 64p so you end up with £8.06
postage includes packing materials however if you overcharge on postage you will get bad feedback my personal suggestion is you add no more than 15-20p to actual cost, royal mail small parcel with label purchased through ebay costs £2,85 ( it is 2.95 at post office) and gives you a tracking number so you can print it at home.
Anything bigger than small parcel size (45 x 35 x15cm and upto 2kg) is cheaper by courier
if selling clothes place on coat hanger on the back of a plain white/wooden door or against a white sheet make sure nothing else in photo no perfume bottles mugs etc, if clothes take photo of label that says make, brand and size and say if it is dry clean only
selling things for 99p is not worth it
look at sold prices for an idea of prices as you are a new seller you will not get the highest prices so if 4 items have sold previously ranging from £7-19 assume you will get £7 and certainly don't start auction at a higher price than £7, if there are lots of them on ebay sometimes a fixed buy it now works best
you need a sensible price good photos, and once purchased they need posting the next day or at a stretch the day after, if doing auctions don't end them on a monday if you can't post till friday
if it has a fault say so, don't say worn once when worn a dozen times people like clothes from smoke and pet free homes so mention this if true
if it is just something that can go in a mailing bag ( a 10p bag for life inside out will do) then I think it's worth it if sells for £4 plus if it needs a box bubble wrap and packing peanuts it needs to sell for £10
I sell a lot of china, I know how to pack to avoid breakages assume your parcel with be dropped from shoulder height onto concrete pavement it needs to survive