Making a chute for cash to go into safe through wall

I need to make a chute to go through a 12cm lath and plaster wall in a Victorian house.

At the far end will be one of those cheapo small safes with a keyboard for entry of a code to open it. The safe is currently on a shelf and screwed to the wall.

The other end of the chute will be positioned behind a picture to hide it.

I guess the chute needs to be sloped downwards to discourage the bags of coins and bunches of cash from getting stuck on the way in.

This isn't a particularly high security environment so no need for spikes inside the chute to stop people trying to fish stuff out!

I'm planning to take a square of metal out of the back wall of the safe with an angle grinder where the chute joins the safe.

I reckon the chute needs to be about 6cm high and 10cm wide - not as wide as a letterbox. It probably needs to slope down at about 45 degrees.

I'm planning to cut through the first bit of plaster and laths with a multi tool and hope I'm not near one of the studs, then come through on the other side in a similar manner but further down to allow for the slope.

I'll probably have to make the chute out of MDF but can anyone suggest a suitable pre-made chute material? Maybe the kind of pipe used to vent extractor fans?