You'll find more folks with direct experience with a range of inflatables (and folding kayaks) over at the folding kayak forum:
Having spent my first 4 years of sea kayaking on another Great Lake and also being familiar with Lake Erie having lived in Western PA most of my life, I have to join with the others in strongly urging you to reconsider any plans to take a cheap inflatable out on one of our inland seas. In fact, when I was living in Michigan, the Coast Guard at one point got so tired of having to retrieve kayakers in incompetent boats who were swept by wind, waves and offshore currents out beyond where they were able to get back to shore, that for a while they were intercepting and banning paddlers in rec boats and inflatables from venturing into the lake in some busy coastal areas. It can be a real challenge to regain the shore on a windy day in a competent sea kayak -- trying to drive a bulky and bargelike inflatable in is next to impossible.
You can NOT predict what will happen on Lake Erie, or any other water body of that size so don't kid yourself about "only going out on nice days". Did you not hear about the father and young daughter who drowned near Cleveland two months ago after venturing out on a "nice day" in a recreational kayak? I have seen the conditions change within minutes on these lakes. In fact, 2 of my cousins, who had grown up on Lake Michigan and swam in it daily during the warm seasons, both drowned one awful day 20 years ago when a storm materialized out of nowhere while they were body surfing. The sky turned from blue with fluffy white clouds to violent grey and the water went from gentle waves to howling wind and screaming surf, sweeping them away from the sandy beach and smashing them against the breakwaters.
As others have said, whitewater rivers and open sea are two entirely different beasts. The features that make inflatables suitable for rapids go against them on windy open water.
Another thing that you have to consider in paddling Erie is water temperature. This isn't Florida. The lake rarely gets up even to 70 degrees and in some summers never goes above the 60's. Average temperatures in June are in the 50's. Even in the 60's your autonomic responses are drastically reduced and you can become unconscious if immersed for only a couple of hours. Long before that you would become incapacitated enough to not have the strength to get back in your boat in a capsize in rough water. A closed sit-inside kayak is usually the boat of choice for cooler waters because the sprayskirt keeps your lower body from getting doused. Rec kayaks, besides being short and wide (which makes them a danger in strong waves) tend to have oversized cockpits which cause a spray skirt to implode.
One viable option that would be safe for what you are planning would be folding kayaks. Their rigid frames make a craft that is less susceptible to wind and faster and easier to paddle. Probably the most budget friendly of the seaworthy for someone your size would be the Pakboat XT-15 or Pakboat 155. Both are sort of folder/inflatable hybrids in that they combine a rigid aluminum frame with inflatable side sponsons that keep the skin tight and add flotation. They are light like inflatables and pack down to fit in a car trunk or closet. You also have the option of paddling them with or without the deck, which is removable. You can get a new Pakboat for around $1500 and sometimes they come up for sale used. There are also free instructions for building your own sea-worthy folding or inflatable kayaks at the Yostwerks site (thousands of ordinary people have built them, as you can see in the Gallery on the site).
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