I don't even want to think how much the arcadia pendants he'd need would cost new for 4X 400ws. Sooo...I'll go look instead of thinking cause I'm curious. Let's see, from www.aquaria.com.au...
a tunze MH 400W is $1770 each X4= $7080 au=$7500 NZ
Geisemann, about the same: $6672 au=$7092 nz
Arcadias don't seem to have a 400W version sold on there so, for equivalent wattage,2 Arcadia Series 3, 3X250 = $5776au=$6140nz
Not including shipping and whatever and any cheaper sources pies could possibly get them from.
DIY would be like $800 for 4X400 and I'm sure you could get a really nice surround or something made for them for far less than another $5K.