A single PC CPU core is running at roughly 3 GHz. Both hash functions and stream ciphers exist that operate at around 1 cycle per byte (with long messages). A brute force attack on a key requires computing at least one block, which we can call 128 bits, or 16 bytes.
So about 200 million tries per second per core, or call it billion per CPU. A GPU has about ten times the computational power of a whole CPU, so that would be ten billion per second. (Those are almost an order of magnitude more than Bitcoin hash rates, but a fast cipher might be close.)
So a billion operations per second is something even your typical script kid can probably do. That allows breaking 50-bit security level in a week or two, and 56-bit in a year. A small cluster or botnet could multiply that by a couple of orders of magnitude. 64 bits is not necessarily secure against an adversary with some resources to throw at you.
After that the math becomes fuzzier. Can a state-level adversary break 80-bit resistance? Maybe. If not right now, probably in a few years or decades. 90 bits? Maybe not, but possibly in the future. 100 bits? Remotely possible to reach in the future. 112-128 bits? The top end is essentially enough against any classical adversary.