This isn't hard to do. This is how I'd do it:
First off I'm assuming this is for your car listed in your name, and does the usual GM method of controlling signal/brake lights (the signal and brake lights are shared, so when the brakes are applied at the same time as the signals, the one side signals and the other side stays steady).
You need the 4017, 3 set/reset latches, a 555 timer for the clock, AND and XOR gates and some transistors & relays to handle the load (lights).
Outputs 1-3 of the 4017 connect to the SET pin of the latches. So when each output of the 4017 goes high, the latch turns on. The outputs of these latches would go to a transistor to switch on a relay.
For your blinkers to flash, I'd connect output 4, 5 or 6 (depending on how much time delay you want) of the 4017 to the RESET pins of the latches. So the lights turn on in sequence and then all of them turn off at once.
You could use your turn signal switch as the input to enable the clock of the 4017. Make sure to debounce the switch input.
You need to make two identical circuits since adding the extra relays and logic to allow only one circuit would be just as complex (if not more so).
That takes care of the flashers, but the brakes are a little different. To get the brakes to work, you need to make sure the 4017 doesn't get to reset the latches by freezing the clock input after the first 3 inputs have come on (your hold function). So you need an input from the brake switch along with output 3 of the 4017 and you want to make sure when both of these are high that the clock is disabled. An AND gate for these two inputs plus an XOR on the clock enable (one input to the XOR is your signal switch input and the other is the output of the AND gate) should do it.
If you want to get even fancier, you could use AND gates on all three latches. The outputs of the latches are one input and the signal/brake switch is the other. This way, the instant you let off the brake (or cancel the signal lights) the output would switch off immediately instead of waiting for the sequence to end.
Now after reading all that, I think if you could find one for $80 that does everything then I'd probably go and buy it.