How many of your competitors are using the sponsored/enhanced listings? The more of them there are, the less "special" the paid for listing is, so if there's more than about 4 or 5 don't bother, you'd probably be better sticking with the free listing and let people choose to call you because you have a local number.
If you do go for it do it small-scale first year, if it doubles your money consider stepping it up next time. You can use another address in another town as an add-on listing at a lower price than the full one, all you need is an address and postcode but it isn't displayed on the web page so won't confuse people about your actual address