With Alumilite White, once the two parts are poured together, I have three minutes to mix and pour into a mold or molds.
I used to do a fair bit of resin casting. I had one pack of Alumilite and I didn't finish it before it went bad - I didn't like the stuff at all. It was more expensive than the stuff I ended up preferring, and didn't give such good results.
My recommendation for home casting on a budget would simply be to use a different resin with a longer open time and if possible a lower viscosity. Then you can be more gentle with the mixing so you start with fewer bubbles in the mixture, and you have longer to ease the bubbles out with tapping or vibrating or whatever you choose to do. The lower the viscosity the easier it is to get bubbles out, too. This adds to the de-mould time, but unless you're doing production runs that's probably not a concern for the home caster.
You can make a fairly decent vibrating table with two bits of plywood, sandwiching springs over some bolts in oversized holes, then hot-glue a small electric motor with a off-centre weight attached to the top part.
(Unfortunately the one I settled on isn't available any more from the place I used to buy my resin-casting supplies, and they rebadged things under their own brand so I don't know who actually made it. Plus I'm in the UK, so who knows if it's available in the US.)