This week I needed to send 21KG of motorcycle parts to a mate from Leeds to Cumbria. As I didn't really require insurance or proof of delivery I went with RM std parcels but there was one hitch....the max weight they carry is 20kg (& max 1.5m long by something like 1m width).
In the end I had to split the parts, one lot weighed 17KG and cost £12.xx and the other bang on 4kg and cost £7.70
In essense if you can make each parcel between 10KG & 20KG (and within size limits) and dont need proof of delivery/tracking then it'll cost £12.something by RM std parcels