bar·gain 
(bärgĭn)
(bärgĭn)n.
1. An agreement between parties fixing obligations that each promises to carry out. See Synonyms at agreement.
2.
a. An agreement establishing the terms of a sale or exchange of goods or services: reached a bargain with the antique dealer over the lamp.
b. Property acquired or services rendered as a result of such an agreement.
3. Something offered or acquired at a price advantageous to the buyer: That silk dress is a bargain at that price.
v. bar·gained, bar·gain·ing, bar·gains
v.intr.
1. To negotiate the terms of an agreement, as to sell or exchange.
2. To engage in collective bargaining.
3. To arrive at an agreement.
v.tr.
Phrasal Verb: To exchange; trade: bargained my watch for a meal.
bargain for (or on)
Idiom: To count on; expect: "I never bargained for this tearing feeling inside me" (Anne Tyler).
into/in the bargain
Over and above what is expected; in addition.
[Middle English, from Old French bargaigne, haggling, from bargaignier, to haggle, of Germanic origin; see bhergh-1 in the Appendix of Indo-European roots.]
bargain·er n.