Corded Recip saw are cheap! plenty of blades to choose from and just make a jig up out of bits and pieces wood etc to hold victim down then can chop up smaller easier.
your better off with a 5" grinder than 4" as there engineering grinder for bench type work so limited discs so if buying another get a 5" gives farm better/longer cutting with each disc and machines are similar size and weight. plus 7" is slightly bigger more power and 2" bigger and not so unwieldy as 9".
Mind 9" is ok if have a jig so both hands on machine.
You can get diamond type discs that will cut soft materials.
Normal discs clog then overheat which can then lead to delamination