Here's a networking quiz for you

Can a managed L2-switch with 802.1q-VLAN-capability be used to segment
the LAN into multiple independent subnets without using trunking?
Ie. in this scenario there's no need for access to the Internet.
Idea is to assign a subnet to each port and attach a cheap unmanaged switch
to the port and attach the devices of that subnet into that unmanaged switch
at that port of the managed switch.

There is only 1 (relatively expensive) managed Gigabit switch with 8 ports,
and 8 very cheap unmanaged (ie. dumb) Gigabit switches with 8 ports each.
So, a total of 8 subnets with up to 7 enduser-devices (ie. PCs) in each should be possible, totaling up to 56 enduser-devices.
Access to the other subnets, if desired, would be configured via network routing table entries.
The 8 subnets: for example 192.168.1.0/24 to 192.168.8.0/24

Is this doable with such a managed switch using VLANs, or should one take an 8-port router instead?
Has anyone already did such a similar setup?
Which solution (switch or router) is easier to perform and easier to maintain/support/administer?

School question of some sort ?
Sure a L2 switch can be use to "segment" your LAN somewhat in the way you describe, but you will loose quite some physical ports.
"Trunking" is only applicable for the "uplink" part. If you do NOT want any form of trunking, the only way is to "uplink" 1 physical cable for each VLAN in stead of "combining" multiple such VLAN's on a trunk. On a given switch a port containing an actual andpoint can only be part/member of a single VLAN.

More important : who is doing the L3 part ? What device is responsible for L3-traffic on the 192.168.x.y subnets ?
If the "managed" 8 port switch (the more expensive one) cannot do L3 you have a problem and you need indeed a 8-port router of some sort (or L3-switch)! if you do not want to use any form of trunking. (managed switch does not always mean L3-switch)
Without a device working at L3 you have no concept of networking/routing/subnets to begin with. VLAN's cannot provide that for you.
VLAN's is only grouping some ports together to make a small broadcast-domain (aka switch)

Eg. a Mikrotik RB3011 would be fine for that. You would take 8 ports, on each of the ports you configure 192.168.1.254 , 192.168.2.254, 192.168.3.254 and so on. You run 8 cables down to your really dumb L2-8port switches etc voila. Done.

@jvanhambelgium, you are absolutely right. The key here is "L3" (ie. a L3 switch), or a router (=L3).
With a managed L2 switch alone this can not be done.
On the web there is much misinformation regarding such subnetting via VLANs.