{Perish with thee} (sun soi ei(8820)eis ap(936c)eian). Literally,
Be with thee for destruction. Optative for a future wish. The use
of eis with the accusative in the predicate is especially
common in the LXX. The wish reveals Peter's indignation at the
base offer of Simon. Peter was no grafter to accept money for
spiritual power. He spurned the temptation. The natural meaning
of Peter's language is that Simon was on the road to destruction.
It is a warning and almost a curse on him, though verse  22 
shows that there was still room for repentance. {To obtain}
(kt(8373)thai). To acquire. Usual meaning of the present tense
(infinitive middle) of ktaomai.