General:
* Deal
* Offer
* Sale
* Discount
* Reduction
* Steal
* Good buy
* Great value
* Affordable
Informal:
* Snag
* Score
* Rip-off (used ironically when something is a good deal)
More formal:
* Agreement
* Negotiation
* Transaction
* Contract
Other options:
* Compromise
* Concession
* Trade
* Arrangement
The best word to use will depend on the specific situation and the tone you want to convey.