The phrase "are mostly expensive" is correct and usable in written English.
It can be used when discussing the general cost of items or services, indicating that they tend to be high-priced.
Example: "Luxury cars are mostly expensive, making them less accessible to the average consumer."
Alternatives: "tend to be costly" or "are generally pricey."
Gifts are mostly expensive silk carpets, gold and silver items, drinks, caviar and money.
But phablets are (mostly) expensive, so which one is right for you, and do you really need to spend £600 or more?
The games are (mostly) expensive.
This index as the key indicator of process performance is normally determined by offline sample analysis in laboratories or online hardware analyzers that are mostly expensive with high maintenance costs.
Traditional metal-removal techniques from water such as precipitation, oxidation, reduction, electrochemical treatment, reverse osmosis, solvent extraction, ion-exchange and evaporation are mostly expensive and difficult to apply (Özcan et al. 2009; Kul and Koyuncu 2010; Gupta et al. 2012, Gupta and Rastogi 2009).
The haircuts were mostly expensive, and the shoes peeking out below clean jeans were often of fine leather.
However, like many early technologies, 3D capture devices are mostly too expensive and complicated to cater to the masses.
These methods are mostly ineffective, expensive and produce side reactions, high sludge and by products formation and not suited to degrade all dyes, etc. (Krull et al. 1998; Verma and Madamwar 2003).
This meant that Apple's share fell from 43% to 34%, though remember this is units, not value and Apple's wearables are mostly more expensive than its rivals' products.
Commercially available HRM analysis systems are mostly proprietary and expensive.
Common methods to enhance the reaction rate of aluminum and water are the application of alkaline conditions or amalgamation for aluminum activation to produce hydrogen [19, 20, 21, 22, 23, 24, 25, 26], yet the corrosiveness of the alkaline media is a major problem for the reactor, and the chemicals required for the amalgamation process are mostly toxic and expensive [14, 18, 27].
