No one can accurately answer this, as the price or value of a model is subject to the normal laws of supply and demand. I guess the true answer is that your model is worth whatever someone is willing to pay for it. Some collectors will pay a premium to get the one model they are searching for, while others may not be that interested and hence pay a lower price. As a guide though, there are really just two main factors that will govern the price, they are:
1) The rarity of the chosen model
2) The condition of the model and its box.
The highest prices are afforded to those models that are in mint boxed condition. That is the models must emerge from their boxes as fresh as the day they were manufactured and the boxes must be pristine and free from fading. Any deviation from this ideal will drastically reduce the value. Unlike some die-cast models, refurbishing a model by touching up chips etc. is a definite no-no and renders a model virtually worthless.
If the model no longer has its original box then the value may be reduced by as much as 50% that of a boxed example. Of course there are some exemptions to this, particularly rare examples, for some standard early models this can mean that the box is worth over AU$100.
Guide books such as the MICA White Book, Charlie Mack’s or John Ramsay’s price guide give an indication of dealer ‘values’ i.e. the amount of money required to purchase the model from a dealer. The values given are for mint boxed examples only. These are values that probably should be used for insurance purposes.
There will also be some regional variations in the cost of a model. For example only a few first series Yesteryear models were originally exported from the UK and therefore tend to be scarcer in the American and Australian markets and hence in those areas you may pay a slightly higher price.