It is important for musicians and music lovers to support the conservation and preservation of natural resources used in bow making and instrument making. Many such resources are becoming endangered and restricted. For example, the tree species, Pau Brasil or Pernambuco, that is regarded as the best wood for bowmaking is very much endangered and has restrictions on its harvesting and sale. If such a resource becomes unavailable this would have a detriment impact on the traditions of bow making and music making. Supporting the conservation of such resources helps preserve the tradition of instrument making and music making. Please consider supporting this effort by visiting the Alliance-International website for ideas of how you can help. www.alliance-international.org/
Buying a cheaply made inexpensive bow or instrument is not a good investment and often supports businesses who are less responsible in their use of resources used in instrument and bow making. Quality matters even for an entry level bow and instrument. Invest a little more to get a bow that is made with care but still affordable and worth maintaining. Such a bow is a good investment of your money. In general, expect to pay at least $100 on an entry level bow and look for one from a business that specializes in bowed strings.
As a rule of thumb, I recommend steering clear of "new" bows and instruments sold for extremely cheap prices online. Corners are cut to bring the prices down so low and the quality and the playability of these instruments/bows is truly terrible. Cheaply made bows are also difficult if not impossible to rehair. Many who service bows don't even bother rehairing these poor quality bows which means leading the consumer to buy a new bow when a rehair is due.
Low quality instruments also inhibit learning for students because they are difficult to play. For someone beginning a stringed instrument, affordable instrument options can be found that are set up well and made to be easy for a beginner to play. Violin shops are great for finding quality instruments for violinists, violists, cellists and sometimes bassists. There are also bass specialty shops that have much needed quality instruments are services for the double bass.
I recommend consulting your string teacher and your local bowed string instrument shop, often these shops have the word "violins" in their name. Shops that specialize in specific instruments such as basses or cellos are also a good option. General music stores sometimes carry decent bowed string instruments but I wouldn't bank on it in every case.
Good quality bows can be found on places like ebay or reverb but you need to sift through the low quality ones and you need some experience to know what you are looking at.