You're in luck. There are plenty of great rain pants out there. For fit, you have three options.
One, shop around a bit to see how different pants are cut. Arc’teryx, for example, says their Large/Short pants have a 30.5” inseam. They may work well.
Two, have them modified. Your local Mountain Equipment Co-op store should be able to tell you where they send Gore-Tex items for repair. (Just whacking 4” off the cuffs isn't a great idea, so try to find someone who can remove a section, re-sew, and tape the seam.)
The cheapest solution is to make do with rolled-up pants. Not perfect, but it'll work in a pinch.
Now, what to buy? At the low end, price-wise, you’ll find Marmot’s Precip Full-Zip Pant ($95). The Precips are lightweight, with a full zipper that makes putting them on and taking them off easy, and a proprietary waterproof coating that will keep you dry and allow for decent breathability. They also come with an interior coating that helps prevent condensation from building up and creating a clammy feeling.
The Best Summer Rain Pants: REI Kimtah Pants
REI’s Kimtah Pants ($189) are a step up in price, and they’re made with a waterproof-breathable fabric called eVent, a material I really like. REI says they'll stay windproof up to 60 miles per hour. They have sealed seams and ankle zips and grommets where you can add instep cords, giving them a snug fit around your feet. They’d be good for just about any activity.
The Best Summer Rain Pants: Arc'teryx Beta AR Pants
If money isn't a major consideration and you simply want the best pants, take a look at Arc’teryx’s Beta AR Pant ($350). Made with Gore-Tex's windproof and waterproof Pro Shell fabric, they're durable enough to take skiing and light enough for backpacking. With special patches sewn in to prevent abrasion and Arc’Teryx’s always-impeccable construction, they'll also last for years. I rarely wear rain pants while cycling, but these would work for short rides in a heavy downpour.