A fee added on top of the regular price, such as for special services, peak times, or premium options.
An extra charge applies on weekends.
specially reduced charge; discounted rate
A lower-than-usual price offered under special conditions, such as early-bird discounts or promotional campaigns.
A specially reduced rate applies to members.
割増料金 explicitly means a surcharge or premium added to a base price, while 特別料金 can be either a surcharge or a discount depending on context.
割引料金 unambiguously means a discounted rate, whereas 特別料金 is broader and can refer to either a higher or lower special price.
Compound of 特別 (special) + 料金 (fee, charge).