I am not aware of a direct method for equally distributing your bandwidth using only a router, but you can assign bandwidth priority for certain applications (web-browsers, bit torrent clients, etc) and that way make sure that you have enough bandwidth to surf.
Have a look at this article it will give some ideas on how to achieve priority based bandwidth management for applications by configuring the QoS ruleset of your router. The article does recommend a router too but you can also look for other routers with the same specifications as the router could be an outdated model.
(Also you can get a refurbished or a used model of the router mentioned in the article for around 50 bucks but I haven't checked up for other models in the same price range.)
Another option is using a firewall OS, you should have a look at PFsense and this article. It has very meager hardware requirements, or you could set it up as a virtual machine (if you don't want to invest in separate hardware for this project) in your own computer and that way all you will need to invest in will be a 1 or 2 extra network cards (depending on your setup) and a little bit of effort in setting it up on your end.
Here are a few howtos for setting it up as a virtual machine assuming you are using windows:
1) Installing pfSense in VMware
2) Installing pfSense on VirtualBox