In reply to humptydumpty:
do the lorry thing... the ones you list here are all too narrow. The lorry ones are 50mm wide as is normal for every slack line I have ever seen.
I bought mine in Decathalon for about €30 about 3 years ago and it just fine... works out about €1 per m including the ratchet and a bag to store it in.
Im very good at falling off it!
You could get imaginative... search youtube, there are slacklining video bloggers out there who are doing all sorts of interesting things using GriGris to tension them.