wrap in bubble wrap, protect fragile areas or take the mech hanger off and tape to frame then wrap up. If you got a rear dropout/rear stay rptector like the ones you get on aftermarket forks then tape that in to prevent it getting squashed and tape together all the loose bits i.e. headset.
Wrap the whole thing in 2 bin bags and tape with gaffer tape. I usualy post via parcel force and should be about £15 I think of the top of my head – most frames will come inside the dimensions – I think 1.5 metre circum and no bigger then 1 metre any dimension – have a look on their website. They can collect it or you can drop it off at the post office.
Done it 3 times now with no probs.