I saw a Harbor Freight blast cabinet laying in a grassy field behind a guy's house, he still had all the parts for it, and gave it to me for $50. For a little bit of money I've made this AWESOME. My costs and parts list below. Parts list has Menards parts numbers, but if you don't have Menards in your area you can still look the part up on their site to see exactly what you need to build the metering valve.

Cabinet: $50
Dust collector: $120
Metering valve components and hose: $28
Dust collector baffle: $20
Dolly casters: $16
Gloves: $30

The dust collector (currently unavailable): https://www.amazon.com/gp/product/B08...

Parts for the metering valve:
hose barb 1/2 ID x 1/2 MI 6801850 ($2.99)
1-1/4 x 1 reducer washer 3655726 ($0.98)
1" chase nipple 365582 ($2.18)
1" Galvanized tee 6858748 ($2.79)
1" galvanized plug 6858777 ($1.29)
1 x 4" Galvanized nipple 6858117 ($2.29)
1" rigid threaded coupler 3656134 ($2.78)
1x2" galvanized nipple 6858094 ($1.39)
1x1/2 galvanized coupling 6855194 ($1.99)
1/2" ID x 10' vinyl tubing 6840455 ($8.59)
3/4" hole grommets 3642973 ($1.49)

Also needed will be some sort of small ball valve to tap into the metering valve to allow air mixing.