Baking – Anybody know where I can get some Stanley spatulas

This is the cheapest chamber vacuum sealer that I've come across: VacMaster VP112. At $669, it's half the price of most other chamber sealers. Chamber models are far more "professional" than the stuff marketed to the home, and my understanding is that they are far more reliable.

The difference between a chamber model and a home model is that you place your food in a bag in a chamber. The entire chamber is used to create a vacuum, meaning that liquid won't leave the bag. A home sealer will also not go below atmospheric pressure while a chamber unit can get a much higher vacuum allowing for vacuum marination, compression or fruits, and better flavor penetration during sous vide, which may or may not hold any interest for you.

In terms of your specific questions:

1. My understanding is that these consistently make a good seal.
2. I can't speak to longevity, but these are the kind of units that restaurants use for sous vide prep, so I assume they take a beating in those environments.
3. Because it's in a vacuum chamber, liquid is no problem, and you can actually vacuum seal just liquid.
4. Major Fail. These things are big and heavy. The one I mentioned is 24" x 16" x 9" and weighs 53 lbs.
5. Shouldn't fail to seal. Not sure about waste if it does.
6. Cannot be used with a container, but why would you need to rather than using a bag?
7. Minor Fail. The model I listed is a little over your price range. Most other models of this type will be between $1,250 and $7,000.

The other consideration is chamber size. You obviously can't vacuum pack anything that's larger than the vacuum chamber. The one is listed has a chamber size of 12" x 11" x 5".

Charging a whipper two or three times is definitely not going to make it explode; for certain lower-density preparations you're supposed to charge it twice, but even if that weren't the case, consider that one of the chargers holds only a fraction of the volume of the whipper itself (8 g, to be exact), so if the chargers don't undergo explosive decompression then it's definitely not going to happen to the whipper.

As for it possibly turning into butter, that's a more realistic possibly depending on what you're putting inside it. I can't verify whether or not it happens with cream since I've never tried it and probably never will; I wouldn't recommend it, since whipped cream gets very dense to begin with.

But honestly I think your biggest problem is going to be that whipped cream dispensers aren't designed to dispense upward. The instructions are very explicit that you have to hold it upside down in order to dispense; if you hold it right side up then it's just going to vent the gas and make it impossible to get the cream out with opening it up.

Simply stated, the cream is much heavier than the gas, and I believe that whippers don't actually achieve saturated vapour pressure inside. That's why the gas will always eventually end up on top no matter how you orient the whipper; the key to getting the cream out is forcing the gas back down through the cream by depressurizing it, which is why you need to hold it upside down.

So unless you want to eject it from the bottom of the cake, I'm sorry to say that I don't think this is going to work for you.

One alternative you might be able to try is to pre-whip the cream with a stabilizer or make a fondant, then put it into a hollow tube and eject the gas from the whipper into that tube. That way you can guarantee that the "liquid" is actually in the path of the gas, and the gas should propel it upward. I emphasize should; it's going to depend on the density of what you're trying to propel and how good your seal is, and you'll probably have to experiment a little.