Just my opinion, but there are very few things that a normal auto shop can repair on a Prius, other than the obvious brakes, tires, oil changes, etc. Almost none of the ICE and hybrid module parts are available from anywhere other than the dealer. And, the older Prius's are even worse; because there were less of them made.
Oil and air filters can be found at AutoZone, Pep Boys, and other parts places, but even a water pump and other relatively simple items can only be found at a dealer, or a junk yard.
Since even dealer service departments have trouble with repairs, it is really unlikely that a regular auto repair shop will be able to do much for you. If they do attempt anything under the hood, there is a good likelyhood that you will still end up at the dealer to fix what they did.
Again, just my opinion: I'd take all that money you saved on gas, tires and relatively few repairs done so far, and take your Prius to a Toyota dealer. At least you can be assured you will get the correct parts and they will work on it until it is fixed.
Otherwise, you probably won't need any major work done until the 120,000 mile scheduled maintenance, which includes some relatively expensive items. And you may be able to do some of those yourself.
By the way the ICE uses a timing CHAIN, so you won't need to replace a timing belt. But, the serpentine belt probably is original equipment, and there are some non-routine fluid changes (ICE radiator and hybrid coolant system, transmission fluid, etc.).
The 5,000 mile service is a good idea. For the cost of an oil change and tire rotation (around $50), you can get some good background info on your vehicle. And, they will check it over thoroughly. Just make sure to take some time to evaluate the inevitable repair list they will give you. Some of the items are not required, but just extra profit for them. Also, opinions vary, but I personally don't think that paying extra for "flushing" any fluids is cost effective. Changing fluids regularly (per maintenance schedule) is all Toyota recommends. The "flushing" process is a profit generator for any auto shop.
Can you describe the "loud" sound you hear? That is unusual.
Some new Prius owners complain of loud engine (ICE) noises, etc. However, the Prius is so quiet, that most sounds are more intrusive than when experienced in other vehicles. In fact, most other cars are so much noisier that some of the sounds you hear in a Prius wouldn't even be noticed above the regular background noise.
I still find it amazing that regular cars run the ICE when idling at a stop light. What a waste of fuel. And, I know that the technology exists to shut down their engines when the vehicle isn't moving, because there are a couple of GM vehicles that do this.
In any case, is the loud sound coming from the ICE, or when or under what conditions do you hear it?
I found some correspondence on the steering rack, and it said that it extended the warranty on this item for five years, unlimited mileage. So, it looks like your Prius is even outside the extended warranty on the steering rack.
If you have had this vehicle serviced regularly at Toyota dealers, you may be able to get them to absorb part of the expense as "good faith". They have done this for some in the past, and often split the cost, which would save you some money.
Alternately, you might be able to find a used part on the Internet or local junk yard; although, personally, I wouldn't do this.
Again, I'd ask the Toyota dealer if there is anything they can do to help out with the repair cost. It doesn't hurt to ask -- All they can say is NO, and you are no worse off. Also, ask to talk to the Toyota factory representative or zone manager. As I said before, they may go halves with you or perhaps even absorb the entire cost. This is a safety issue, and Toyota really doesn't want any bad press about this failure or high repair costs. There might even be a "silent recall" that isn't offered unless you escalate the problem. (If you are willing to pay the entire cost, they won't offer to help.)
Sorry to hear the outcome. If you have a trustworthy mechanic, you might want to search for a replacement steering rack on the internet or though the junk yard suppliers. I know there are a couple of Toyota dealers that sell at a discount on their Web sites. One is the Toyota dealer in Sparks, Nevada, that sells a lot of Tundra parts on another Toyota forum.
Plus, keep us informed on your progress. There are still a few classic Prius owners on this site that would be interested in how things turn out.