to buy

Let us take a look at " to buy":
The Germanic words are suspected to come all from Latin.
German. "kaufen", swedish "köpa", Old English "ceaipan", Mhd. "koufen",
Ahd. "koufon", Gothich "kaupon".
All these words are supposed to be a derivative of Latin "caupo", a
derivative of the Latin verb "cauponari"
The Slavic should know this word too since we have "kupa, kupi, kupati,
kupiti".
The romance languages as George suggested have as follow:
Port.:comprar
Spanish:comprar
French: acheter
Italian:comperare, comprare
Rom: cumpãra
I would accept the etymology of a Latin root if there won't be the word
for " expensive" which means in Rom. "scump".
The word "scump" is given as coming from Slavic "skonpU" by my DEX
But is a "skonpU" in slavic? I know just "skupo" but my knowledge are as
usual limited, so I try to make a search on the web for finding out what
about:
Russian: dorogoi
Serbian: skupo
Bulgarian:skUp
Polish: drogi
Ukrainiean:dorogui
It seems the form with "skup" it is just in south slavic to find. Just
there?
There is of course in Romanian . But what about Albanian? I have no idea
if there is something in Albanin which will fit into this equation. OK,
so the form with "sku(m)po" is to find just in south Slavic and in
Romanian.
The south Slavic forms are explained trough lost of nasal I guess.
So the supposed Slavic "skonpU" > skupo in Serbian, and "skUp" in
Bulgarian. Why did not Romanian lost the nasal?
It is said that specialy "n" before consonants " get los in Romanian in
the Latin words:
conquerreo > cuceri, so it should have been very easy to lost the nasal.
The explanation is given as " the phenomenon ceased" as the Romanians
got it from Slavic. Did it? It seems we have 200 years where it happened
a lot of stuff or there is no Slavic "skonpU" but a loan from Romanian,
with the lost of nasal in Slavic.
An another argument should be the "u" here. In Romanian we have o > u
before nasal, so if there has been a "skonpU" then the Rom. form is
regular but the Slavic, does the south Slavic make too an "u" from "o"
before nasal? Or the "o" becomes an "u" before "p" ?
In this case , if the Rom. word "sump-" is not a loan from Slavic, then
it is very hard to accept the another (s)cump+ ara to be a derivative of
Latin even if the Romance forms are too with a nasal there .