You have to discount the costs by the chance of enforcement. Discounting by risk is then the prospective cost, excluding transactional costs. If your potential liability is $5m for breaking the patent, but the chance of enforcement is only 1 in 10,000, then the prospective economic cost is $500. If executing a patent search costs more than $500, then just don't do the search. You might say that individuals don't think this way, but we do at least behave this way; and venture capitalists, with dozens or hundreds of investments do think in terms of probabilities and risk.
How many times have you turned around on a side street by poking the front-end of your car into someone's driveway? This is trespass, and the owner could sue you. But a court would probably only ever award a one-time offender $1 in damages. If a chance of suit is 1 in 1,000,000, then your cost is infinitesimal, and taking the risk is absolutely worth it. That explains why you never think about it. If the potential repercussion was death, you'd be doing a heck of a lot more curb-side three point turns.
The fact that you could be sued, and that it would be absurd in the grand scheme of things to actually be sued, doesn't mean we should modify the property regime to take this into account. There's no need to write in an exception for using driveways to turn around. The fact that enforcement is not absolute, and the limit of damages proportional to some real economic value, solves the problem for us. The homeowner will only sue when his potential return is worth the effort; and the fact that he's oblivious to most driveway incursions is significant as well--it's manifestly evident that he's only going to pursue a conspicuous offender deriving significant benefit from infringing his right.
So, when you speak with a policy maker about the "costs" of patents, you can't simply point to the costs of fastidiously avoiding infringement; how the garage inventor is oppressed by the specter of a corporation suing him in Federal Court. That's because the whole regime is predicated on the notion that enforcement is lax, and on the whole only people for who it's economically worthwhile to seek a license will do so, and conversely patent holders will only seek enforcement on a small subset of infringers capable of paying. The risk of that garage inventor being sued is miniscule, and he knows it; the same way nobody in this thread realistically believes he's going to be personally sued by Bedrock for using Linux.
Patent holders rarely sue small start-ups because it makes sense to wait for them to be gobbled up by a bigger fish, and *then* sue the bigger fish. We tend to think this is an absurdity and evidence of how illogical the system is, but in fact this is exactly how things are expected to work. If the small fish understand this, then it means there's not as much reduction in innovation as we might think. The small fish will infringe, and the bigger fish will expect to be taxed if and when they eat the small fish.
Now, that's the general model. Once you crunch the numbers, of course, most of us would agree that on the whole it's not worth it. Also transactional and collateral social costs (e.g. people overestimating their risk of suit and reducing economic activity more than what is warranted) can overwhelm the social benefit of the system, but it's not as easy to show as one might think.
This entire analysis applies equally to the real property regime. Once you start to break real property interests into all the different kinds of estates, like life and leaseholds, and interests, like tenancies and contingents, then the complexity explodes from the trivial model you're implying. And, again, it works because perfection (solving the halting problem, if you will) is not the goal. If it's difficult to determine or enforce a property right, then it will indeed be enforced much more rarely and lightly, and the value and potential costs of that right will be diminished accordingly. Consider that if you sell a house with a warranty deed you can charge a higher price than if you sell a house with a quit claim deed (where you don't warrant clean title). The value of the right to both seller and buyer is diminished by the risk of enforceability of the right.