the best starting point is honestly a good local running store, if you have one nearby. they can watch you run on a treadmill for a bit and see what your feet are doing. this made a huge difference for me when i started training for my first half. i used to just grab whatever looked cool, and i kept getting these weird knee aches after about 5-6 miles. turns out i was overpronating a lot and needed somthing with more stability. the store folks hooked me up with a pair that really helped. it's worth it for the peace of mind, even if you don't buy from them right away. you can at least get an idea of what type of shoe works for you and then look for deals online or a slightly older model.