Here is roughly what I paid based on memory, I already had most of the parts and media, but here is what it would cost to replicate. Most of the cost is media, other than the K1 for moving bed, Shower/TT media could be many different choices which would inpact cost.
Rubbermaid tank ~$60
3" Uniseal for drain ~$8
3" Farmteck ball for drain ~$10
2x 4" Uniseal for flow back to pond ~$12 each
2" Bulkhead for inlet of other pump $4.99
Various PVC fittings ~$30
13 Crates $70 total (4.5" when stacked)
Air pump $69
Air manifold ~$10
Air lines and stones (AES silica diffusers) ~$75
K1 (5cuft) $150
Bio Balls (5cuft) $150
Lava Rock (4cuft) $16
Straps (we have a lot of hurricanes here) $12
~$677