Learn Turkish: Bu akvaryum için pahalıca bir ısıtıcı lazım. - A rather expensive heater is needed for this aquarium.

Pahalı means "expensive." When you add the softening suffix -ca (or -ce / -ça / -çe depending on vowel harmony and consonant mutation), it weakens the adjective slightly. So pahalıca means "rather expensive," "quite expensive," or "on the expensive side."

Why is the word order pahalıca bir ısıtıcı instead of bir pahalıca ısıtıcı?

In Turkish, the indefinite article bir (a/an) almost always comes between the adjective and the noun. So "a rather expensive heater" becomes "[rather expensive] bir [heater]". If you said bir pahalıca ısıtıcı, it would sound unnatural, as if you were emphasizing the number "one" rather than just saying "a".

How is the word ısıtıcı (heater) formed?

It comes from the verb ısıtmak (to heat). The suffix -ıcı (or -ici / -ucu / -ücü) is added to verb stems to describe a person or a device that does that action. So, ısıtıcı literally means "a thing that heats."

Why is there no standard verb like "is" or "needs" at the end of this sentence?