Art has no intrinsic value. The only value of any artwork is the value the artist places upon it or what others are wiling to pay for it.
Diamonds, as an example, also have no intrinsic value. They are priced at whatever consumers have been convinced they should pay. Buy a diamond for $5,000 and walk out of the store, turn around and walk back into the jewelers.... or go immediately to another jeweler.... it's then worth less than half what you paid for it. (Now, the diamond market has a consortium that actually sets values. So, members [dealers] are essentially "price fixing" to ensure they all charge relatively the same amounts. "Spend three months salary on a diamond for her" was a marketing tactic to convince consumers of a value where none actually exists.)
Find the right buyer and you may sell a painting from a (presumably) unknown artist for $1,000,000. But being unable to find the right buyer may mean the painting is worth $20 at the local flea market. Same painting - no intrinsic value.
In addition, demand plays a role. How many are seeking landscape paintings from an unknown artist? How many artists out there are painting random landscapes? Will this landscape painting have more value if sold where the landscape is recognized?
There's no possible way for anyone to place any value on this painting other than the artist themselves or someone shopping for landscape paintings.
The best one could do is shop themselves... see what similar paintings are being sold for and price for that same venue or sales outlet. Unlike commercial art, with fine art time spent creating is rarely a qualifiable figure which can be used to calculate pricing - those purchasing fine art do not care if it took 10 minutes or 10 years to create the artwork.
I am not convinced that the migration from Arts & Crafts was worthwhile. Freelancing, in my experience, rarely deals with these types of situations. Freelancing is far more related to commercial or commissioned artwork. Not really paintings for the sake of painting and afterwards trying to find buyers.
If one were commissioned to create such a landscape painting, then time creating would be quantifiable and used as a pricing factor.