Let function used with Index.

Hogstad_Raadgivning 

This is just a 'cobbled' together solution.  There are standard functions which scan a function over an array and collect the results together.  The problem is that they are only standard if you have a functional programming background and I need time to study to acquire such.  What I did was to wrap the previous formula in a lambda function so that it becomes a single function call, e.g.

= ModelBestλ(5)

= LAMBDA(k,
      LET(
        Found,XLOOKUP(INDEX(Modell, k), t_priser[#Headers],t_priser),
        BestPrice, SMALL(Found,1),
        Utileier, IF({1,0}, t_priser[Utlleier], Found),
        XLOOKUP(SMALL(Found,1),Found,Utileier))
    )

I then set up a recursion passing through the indices in decreasing order.

= ForEachλ(5,ModelBestλ)

= LAMBDA(p,fλ,
    LET(
       mb, fλ(p),
       result, IF(p>1, ForEachλ(p-1,fλ), mb),
       IF(p>1, xStackλ(result, mb), mb) )
   )

 Note, the function to calculate the best price for each model is passed to this function as a parameter.  The other thing I needed was a function to add the new 'model best' to the list of results already accumulated.  For this I wrote xStackλ

= xStackλ({1,2;3,4},{5,6})

= LAMBDA(prior,new,
     LET(
        n, ROWS(prior),
        k, SEQUENCE(n+1),
        IF( k<=n, INDEX(prior,k,{1,2}), INDEX(new,{1,2})))
   )

As I suggested at the beginning, this needs considerable tidying up if it is to respond to adding model types dynamically or to be reusable for classes of related problems.

Hogstad_Raadgivning 

If the objective is to examine the use of the LET function, the following demonstrates the way in which a solution may be built using formula-local names

= LET(
  Found,XLOOKUP(@Modell,t_priser[#Headers],t_priser),
  BestPrice, SMALL(Found,1),
  Utileier, IF({1,0}, t_priser[Utlleier], Found),
  XLOOKUP(SMALL(Found,1),Found,Utileier)
  )

The additional trick is to combine the seller and their prices for the vehicle type into a table and then perform the second lookup to select the best offering.

If the entire table were required as a single spilt range, that would need a plunge into LAMBDA to perform the array of array calculations and collect the results for each.