If you are going to do small castings, I would check into a small electric crucible furnace from Rio Grande. They are normally used for jewelry pours, but I bought the biggest one and use it for brass and aluminum pours in lost wax/plaster. You can use this on top of a table, although I would suggest it be a metal top table.
Look at their catalog and videos, and you will be impressed.
Now, go down to a local jewelry supply shop, and ask to see their used equipment. Most jewelry and lapidary supply places have shelves set aside for used items that were traded in on better or bigger equipment, or the items are from estates and the family is liquidating them. These are a good source of relatively cheap equipment, the only drawback being most of it will NOT have a warranty. The good news is that any reputable shop will have checked out the equipment and they will make sure it actually works. You can find the same stuff as in the Rio Grande catalog (It may even be equipment from them)
If you are thinking about a larger furnace, such as an induction furnace, you will have to modify the power that comes into your house. Industrial power
(480 volts) is what is normally used in induction furnaces, and they use a LOT of power. The key thing is they melt in a couple minutes, whereas a gas or propane furnace takes 20 minutes to heat a pour aluminum, and 30 minutes for brass.
I have seen some amateur-built induction coils, but I don't know how successful they have been. I think most of them use two 12 volt batteries in series, for 24 volts, but I don't think they will melt very much.
The good news is that 480 Volt power is really cheap. Power companies love to sell that power, and most industrial users are set up for it.
HOWEVER, you will probably have to have it specially installed, and then you will face a minimum charge each month for the 480 volt power.
Unless you are going to pour all the time, and you are going to sell a LOT of castings, it will not be worth it.
I have the same problems as you, except for me it is the summer heat of 120 degrees. I really don't want to pour in that heat, so I either try and pour in the off season (In Tucson, October through May) or if I have to pour in the summer, I pour in the early morning, using my gas foundry furnace.
If you only want to do small castings, or you want to do a bunch, but one at a time, you can start with as little as a propane or acetylene gas torch with a rosebud tip, and a small hand crucible from the same jewelery supply stores I mentioned above. You can buy a small amount of casting sand from Rio Grande, (They sell a sand called "Delft Casting Sand" (It is so fine, that it will pick up fingerprints when you mold it. I poured a speedometer fitting for an antique car with it, and not only did the "Stewart" logo come out, but also my fingerprints on one section.) (From a big casting angle, that type of sand is way too expensive to do a large casting with, HOWEVER, for learning and trying things out, it is ideal. it comes in a one or two pound package, and costs about $10-$15 per lb.) If you want industrial molding sand like Petrobond, you will have to buy a drum of it, which is usually 85-100 lbs. of sand. That is how I buy mine.) but with a hand crucible, put a plumbing faucet or bronze pipe fitting in the hand crucible, then put the torch in a holder, and turn it on. Use gloves to hold the hand crucible tongs, keep the crucible under the flame until it melts, plus a minute or so, and then pour your little mold. You can start casting for as little as $100 for all the stuff you need, probably less if you have the torch and rosebud tip already. And it will give you a good taste of foundry work. It's nice to start on a small scale, as a #8 crucible full of molten aluminum can be pretty daunting, unless you have gotten used to it.
Good luck.
