A good heavy duty pair of snips will cut through much thicker material than they are rated for but you will need to take the absolute minimum material off on each cut, for what you want it would be very time consuming and wasteful. If you wanted to trim small pieces cut to roughly the right size then a pair of snips would be ok for that kind of material. For what you want a guillotine is the only sensible option and it shouldn't cost you anything.