It is best to have a quality upright or grand piano to practice on, but because of the maintenance required on acoustic instruments, as well as the expense and difficulty transporting them, oftentimes a keyboard that closely emulates a real piano is a better fit for students, especially as they are starting out. Below are my recommendations for a keyboard and the necessary accessories.
The main specs that you want to look for when purchasing a keyboard are:
Fully weighted keys
The reason that I recommend looking for something around $400 is that usually digital pianos at this price point are able to accurately emulate the touch and feel of playing a real piano, but they stay away from the extra bells and whistles that you only need if you are doing more performing/composing and want more tools at hand. Some of my favorite boards are the Casio CDP line. I teach on a Casio CDP-130 at home, although they can be difficult to find online. I've recommended a comparable Yamaha keyboard below. Whatever you get, be sure to read customer reviews before purchasing to make sure that people were happy with the sound and feel of the keyboard.
If you are the parent of a string student, or a prospective string student, it is a good idea to start educating yourself on instruments and bows. There are so many choices from thousands of providers, and it can be difficult to navigate good choices from bad. As a rule of thumb, you get what you pay for. It is entirely possible to get a full violin set-up for under $40 on Amazon. However, instruments like this, commonly called VSO's (violin shaped objects) will be made of low-quality plastics that will not resonate well, and will not produce sounds that will motivate a student to continue playing. On the other end of the spectrum, historical violins have sold for tens of millions of dollars. The price there still arguably does not match the quality. Anywhere from the $200 - $50,000 range, quality is closely tied to price. Here are some rules when looking at instruments:
Purchase string instruments from reputable retailers that specialize in string instruments. Here, sales associates will be able to assist you in making an informed decision. In Michigan, here are some to look at: