If you want to cut metal on the machine,just find an old mill and add ballscrews and steppers.It may go over budget but it will work.Cutting metal on a woodworking machine may,just,sort of,be possible.That doesn't mean its a really good idea and trying to do it on a machine with a lot of Z travel, with all the consequent magnified play in the system won't help.For a hobby machine that just cuts wood you can do some stuff with a wooden machine.There are some extremely lightweight machines all over youtube delighting their owners,even if they wouldn't be much use in an industrial environment.You just have to be realistic about balancing budget,usage and building ability.The answer is out there once you carefully consider which features matter most.