You don't need an alignment. The change in circumference is very very small. I like
this wheel and tire size calculator a lot. The wheel size (width/offset) doesn't matter, but the tire size does. Here's a comparison of the setup you mentioned:
e: this is the exact setup you're looking at. Stock is on the left and the new ones are on the right. The stuff marked in red at the bottom is what's important for this question. Diameter or circumference. Bigger/smaller wheels will change the geometry of the suspension components, which cause the wheel to sit at a different angle. If they're close, you aren't going to gain much from an alignment.
PS - do it yourself! Like someone up above said, buy the tools. Alternately, buy a case of beer and ask a buddy. Don't be embarrassed about asking. If someone came to me with a 12 pack and said "I need help putting on my winter wheels but I didn't want to pay a shop 40 bucks" I'd be more than happy to help them.