Formal:
* More affordable
* Budget-friendly
* Cost-effective
* Economical
* Inexpensive
* Lower-priced
* Value-priced
Informal:
* Cheaper
* More reasonable
* A steal
* A bargain
* Good value for the money
* A good deal
* Priced right
Specific to particular contexts:
* Discounted (if there is a sale)
* On sale (if there is a sale)
* Used (if the item is pre-owned)
* Second-hand (if the item is pre-owned)
* Refurbished (if the item has been repaired)
Choose the word or phrase that best fits the specific situation.