Do I have to buy SPF cables for that (and how much)? Can I do It using copper cable?
No. You can use any port and cable (RJ45 copper, SFP/fiber, SFP/copper) to connect two switches together. If the second switch is a managed switch too, you can share any VLAN(s) among selected ports. If the second switch is an unmanaged switch, you can also share a VLAN over all ports of this second switch (but only one VLAN).
To share a VLAN on two managed switches, define the two ports you use to connect the switches as a tagged port and as a member of the VLAN(s) to be shared. This makes the ports so-called »trunk« ports. Then make any other port of the first and the second switch a member of the VLAN it should be part of (so-called »access« ports if they are only assigned to one VLAN).