For our bassinet I just got an old flat sheet that I cut down to size and my mum hemmed for me (since I am crap at sewing). I have also found that bunny rugs fit perfectly as well - so they can serve a dual purpose as wraps and as sheets. Another thing that fits is flannelette flat nappies, if you have any of those (of course depends on the size of your bassinet...). I never bothered to buy sheet sets for the bassinet because it doesn't get used for long enough to justify the cost. For the cot I just got the sheet sets from target or kmart when they were on special - fairly cheap and since the cot gets used for a long time, and my DD has a toddler bed that also fits cot sheets, I figured it was worth buying sets.