> enda þykir mér ráð þetta eigi svo mikils háttar sem þér hétuð mér.

I took 'ráð' here to be the "marriage" itself: "I don't think this is
as prestigious a match as you promised me." MM & HP: "Besides, this
is not as good a marriage as you have promised me."

> Og fannst það á í öllu er hún þóttist vargefin.

This middle voice of 'þykkja' indicates that someone is thinking
something about themselves: "It was quite clear that she considered
herself not very well matched". MM & HP, in more idiomatic English:
"It was obvious that she thought she was marrying beneath her."

> hvorigu mun í þessu kaupi gifta, honum né henni

Not 'hvergi' "nowhere", but the neuter sigular of 'hvárigr' "neither".
Thus: "For-neither will-there-be in this marriage-arrangement luck,
[not] for-him or for-her." In other words: "Neither for him nor for
her will there be any luck in this marriage." Another example of a
phrase split up for emphasis. Neuter is used to refer to both male
and female at once.