third time lucky, what is it with this forum eating posts?
OK, quick version of my long eaten post..
Guide to Korsova has prices for houses by area. From the description Alderns house is a classed as a "house", town houses are described as being the living quarters over a shop.
The prices in Korsova range from 10,000gp to 100,000gp. By their descriptions Korsova is much more over crowded than Magnimar, so I would argue it is cheaper to buy property in Magnimar, let us say 80% of costs in Korsova.
Grand arch district is the middle class area, so I would compare it to Midland in Korsova, which is 10k to 20k. This means I would put it on the market for around 15,000gp, taking into account its location.
Many parties may be tempted to sell a house of that value, another option would be to rent it out for around 75gp per month.
In my campaign I intend for Aldern to have left the house to the target of his obsession in a new amendment to his will. Apart from adding a bit of fluff, this is my way of introducing a bit more gold to my overly large party. As the target of his lust is a hulking male barbarian (Aldern was a bit unusual in his preferences in my campaign) the lawyer trying to explain that the house is his should be fun on its own.