Hi Peter,
If you can wait, and keep a keen eye on eBay there are often Sedgwick 571 Morticer up for sale within the your bracket. The green ones are the oldest, the dark blue and light blue newer, and blue and white are the newest. Sedgwick launch an upgrade of their Morticer this year which adds a few stops for repeat work. I have a blue and blue model which can handle up to 7/8" into seasoned English Oak. The recommended limit is 3/4", however, nothing like pushing the limits.
The machines are built like brick out houses and will last I am sure a life time.
The other options are either a Wadkin or Sagar machine. These again often pop up. If you avoid the vibrating chisel option Wadkins again, both should fit into your budget.
There is a mortiser that has a tilting bed for angled mortises. I think its a Robinson machine, but the memory is a little fallible these days. Anyway I have seen these also pop up from time to time. If I had more space I would have bought one just for the occasional times I need to do an angled mortise. These are vintage machines, but built to last.
A Morticer is a very simple bit of kit, the key to repeatability is having a very rigid frame when you are moving up the wood hardness / size of mortice chisel. If the machine is not rigid enough of there is any play in the sideways, the mortice head will move fractionally causing the chisel to become jammed in the mortice hole. Equally you will not end up with accurate Mortices. I would recommend looking for a machine with a cast column that also incorporates the mounts for the slipping table. Pressed steel will simply not have the rigidity your need for the sizes you are looking for unless as already suggested you do the Mortices in sections.
