Hi,
I write data scrapers as a large part of my day job (I work as an IT project manager for an online retailer). Basically I have to steal data from our suppliers' and competitors' websites, and then use that data to our advantage.
I've had a look at the site you want to scrape, and I should be able to write a scraper for you within 24 hours.
If I understood your requirements - you initially want to scrape the address and sale date of all sold properties, and then weekly you'd like to top up your list with any new (new to the site) sold properties. You also want to scrape properties for rent - again you want the address and the availability date of the property.
To this end I'd sort the properties by listing date, and compare the properties we scrape to the properties already in the database. As soon as we find a property we already scraped, we stop the scraper (it makes the weekly update process faster).
The sold properties scraper should run very quickly - all of the data you require can be gleaned from the listing page. However, for the rental properties, the availability date can only be obtained by clicking through to the property - this makes the initial scrape slow (lots of page requests...). The weekly update should be quick though, since I don't imagine too many properties would be added weekly.
The scraper I would write would be in PHP, and I would hold the data in an SQL database. I'd also give you all the assistance you need setting this up.
John