A bridge is not as "permanent" as implants, it is much easier to replace. Dental implants take much more time to complete including actual surgery involving drilling into jaw bones can be far more involved than a bridge. Implants are far more expensive than bridges.
A bridge lays on the gum and attaches to the teeth on either side. These teeth must be drilled, which is not a good idea if they are not already compromised. An implant fits into a post put into the gum. It doesn't affect side teeth but requires surgery.
A bridge even though it is quite expensive is slightly cheaper than dental implants. The bridge is permanent which is the same as implants. You also keep your own teeth as with dental implants you do not.
A bridge would definitely be a cheaper alternative. An implant can save an adjacent tooth/teeth from being cut for the purpose. An implant always runs a risk of being rejected by the body. An implant should definitely be a stronger alternative.
First the cost. A bridge is cheaper than dental implants, but dental implants last longer and soon they feel like your real teeth. You could feel a bridge with your tongue and it would drive you crazy. And its not permanent, Dental implants are permanent.