If you're not willing to spend a lot on a Unifi based Ubiquiti system there are a number of ways to go on and set up a WDS repeater system consisting of 2 or more access points / routers. In this case these are not routers any more even if you use them since they would not be doing Network Address Translation (NAT). The access points (or routers behaving as access points) will participate as transparent access points and nothing more.
We are planning to add more sections to this article later but first we'll cover Ubiquiti's build in WDS AP-Repeater mode in legace Airmax devices. Note, that this would be structure wise very similar to DD-WRT's or TP-Link's solutions.
The idea is basically linking access points (including the first one in the chain that's getting the internet connection) to each other by their MAC address . Every wireless node (network participant) has a hardware address set in the factory. There are ways to manipulate this but we are not covering that here.
The following is a Wireless setup page of a (now) legacy Airmax Ubiquiti Airrouter. We have to set AP-Repeater mode and set the MAC addresses to connect to. (Unifi systems use their own implementation of connecting to each other so the see this you need older/lower grade access points/routers.) You need to set all the MAC addresses on the access points you want to connnect to with that specific wireless node. Not necessarily all of the MACs on all access nodes, please note.
Depending on the WDS implementation of the manufacturer of course but the more WDS nodes you set the slower the general speed will be. The speed would be also determined by the generally available bandwidth of the wireless node. The 20/40 MHz 2.4GHz bandwidth setting will affect this directly. While we use 20Mhz most of the time for the legacy 2.4GHz wifi band (144Mbps theoretical bandwidth) if you have a relatively noise free area you can try the 40MHz setting too which has a bandwidth maximum of 300 Mbps. (for 2x2 MIMO dual antenna access points)
You'll be getting much slower speeds since we are splitting the bandwidth by using WDS. This is the place where the quality of the manufacturer implementation (and the price of the access point) comes into the picture.