I'm taking the Graduate of REALTOR Institute course for my GRI designation and one of the classes happened to be on taxes, etc. The instructor happened to be a CPA and was mentioning that property taxes aren't actually based on the purchase price of the home, (which is what I had always thought it had been) but actually based on the assessed value of the property. He said you can loosely base your property taxes somewhere between 1 and 1.25% of the assessed value. Which in most cases will end up being near (if not) purchase price anyway, but don't be surprised when the assessed value ends up being slightly different from the purchase price.
For tax information, I would recommend speaking with a CPA, accountant or other more qualified financial advisors.
With a townhome there will also be a homeowners association fee.