It depends really! All I can say about when I purchased the bow for my EUB, is that I spent around £120. Brazilwood with an Ebony frog. Size will make a difference to the price as well, full size, 3/4 etc...mine is a 3/4. Any smaller isn't really worth it, you can't get the length of notes needed!
What I will say though, is that the chances are that budget EUB's aren't going to allow you to bow as well as a better quality one due to the shape of the fingerboard!
The stagg ones for example look impossible to bow on, much flatter fingerboard, there are plenty of users of that EUB on here though, so maybe they can comment!
My Shuker EUB is for sale in the FS section (page 3 i think lol), it's in a higher price bracket, but due to it's true upright fingerboard and bridge, you can bow on it as well as any acoustic double bass.
Hope this helps
Si