A very inexpensive entry rifle is a .499 Hubel Express based on an H&R .500s&w.

These rifles are available in Australia, but getting it rechamberd to 499HE can be problematic. Mine was done by Ed himself.

It's based on the .450NE#2 so it has huge case capacity and can be loaded to the required energy whilst keeping pressures low. Slow to very slow powders will keep the case full enough not to need fillers.

The main problem is the availability of 525gn (or greater) projectiles. The options seem to be make your own in lead or resize some .505 Woodleighs. It has a .500 bore, not the more usual .510 as used in other "500"'s. Maybe if enough people start using it we could convince HRBC or Woodleigh to make some bullets for it.

You will need to add some weight to the rifle to make it more comfortable to shoot.

Btw, for those concerned about the ability of the h&r to handle the pressures.... the original chambering of .500s&w operates at a much higher pressure than the .499HE.