Check out the hitch hiker, I believe wesspur still carries it. It's the cheapest way to convert if you don't already have some of the other gear that a rope wrench set up requires. It's also a really good, well thought out device, it's compact, bomb proof, and you can ddrt with no change over. It can take a bit of experimenting to get it dialed in perfectly to your rope, weight, and style but the nice thing is you don't need eye to eye hitch cords, you can just buy them in 3-3.5' lengths. You will also need a tending point, a piece of small cordage with scaffold knots works great, I have also seen people bend up some heavy wire.
The rope wrench is a great tool as well. In my experience there may be a bit more adjustability than the hitchhiker2 because you can tie whatever hitch you prefer under it.
The unicender is probably the only srt device on the market I haventh climbed on. I will say it's compact and easy to put on and off the rope and seamless to change over to ddrt. Wrapping the rope to descend and the friction points wearing kinda turn me off though.
As far as ascent goes I strongly recommend that you go to a rope walking system. Any foot ascender will do, although I really like the CT. For a knee ascender I don't think you can beat the saka mini from climbing innovations. Super compact and adjustable and by far the least inexpensive option on the market. I don't think you could build your own for much less $.
Tending, the lanyard over the shoulder works but most people prefer a kneck or chest tether. For a cheap chest tether you can take a long loop runner and give it a twist so it looks like an 8, put your arms through so the cross is on your back and clip the two ends at your chest with a carabiner. There are also a few low buck options out there.
I prefer a neck tether and just use a buff with a small carabiner although the options are endless.
