There are three online stores which stock my scenery, including my own:
Which store you use is your choice, you may find it more convenient to purchase from Simmarket if you are in Europe, or Australians may prefer their 'local' store.
Simmarket charges in Euros, and PC Aviator charges in AU$. When a new scenery is first released, I set the price based on the current currency conversion rate for the NZ price, but this can vary a lot over time. Normally this is not adjusted unless there is a substantial sustained change, to maintain a consistent 'local' price in the currency of each store.
The main difference in prices, though, is caused by GST/VAT, the local sales tax. In New Zealand we have GST, but I am normally not registered as my turnover is below the threshold. This could change at some point, but I don't foresee this happening in the near future.
So my prices don't include any sales tax. The other stores may or may not charge a sales tax based on where you live.
Note that you can view prices in my Store in Euros or US$ if you wish, but they are charged in NZ$, so the current displayed conversion will be as close as practical, but may not be completely accurate.