> cheap and easy to find (as, for example, BC 557/567 for BJTs)?

The BS170 n-ch is quite common in circuits. There are more n-ch
than p-ch, unlike bipolars which are found plentifully in both NPN
and PNP. You should have a look through on-line catalogues like
RS, Mouser, Digikey to get an idea of what's around at the small
end (which the BS170 is at). Then you get into the power FETs
like IRF and 2SK types, when parameters like on resistance and
power ratings need to be looked at a little more closely. You can
get a handful of free motor control FETs from old (probably not-
so-old too) HDD boards, for example

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