Just tried a different basket,

3 lots of 7.5mtr 80x40x3 = £146
1 lots of 7.5mtr 40x40x3 = £30
1 lots of 6.1mtr 60x60x6 angle = £40
1 lots of 6.1mtr 60x6 flat = £21

Total inc & delivery = £282

If you can drop down to 80x40/40x40 and redesign the diagonal bracing so that you use some flat and some equal angle for the bracing you should save a fair bit on what you thought.