The value of half a metre of tape is insignificant. The cost in time and postage is what you are really compensating, and you yourself will have to spend time and money to send the trade goods. Do you walk to the post office, or drive, if the latter, count fuel in to cost. Also "bits" does not clearly describe what you are offering. Are you talking about stuff the size of a drinks coaster?
I know that bartering is in your blood
, but it seems that less time money and effort would be expended all around if you just ordered a £5 10m roll and had it delivered.