I have thought through this before, and I have the necessary equipment. This thread is more for /k/, I advise you post there.
Riots in my town are frequent and destructive. You might be able to guess where I live.
A rothco clear riot shield will run you up 100ish dollars. Some used ones float around for 60ish on ebay. Good riot-shields are made from polycarbonate I managed to get a used one from a friend at my police department, they were phasing out the old shields for a newer model, and the old ones worked just fine. NOTE: you can use the round shields, but the rectangular shields are much better as they can be used to prevent a Molotov from hitting your feet.
Next you would want to get some sort of club. Billy clubs and batons are cheap. Expanding ones are not the best to use, try to get a solid baton that is a bit on the heavy side. There are a lot of pretty cheap police batons on ebay, they sell them as "vintage antiques" but they are just fine, just don't get them if they are to old. If you have a little extra to spend, buy yourself a tonfa, they work great in riot situations. Be warned, they take practice to use.
If you want to go the peperspray route, you may have to pay a bit of a heftier price than you would like. A liter of peperspray will cost you about 40-50 bucks, you can get this cheaper if you buy in bulk but it will still cost. I cannot really recommend a brand besides FOX, and even FOX had it's own little fiasco when it switched chemical supplier.
Teargas cannot be obtained by citizens, but it can be made at home. Three parts potassium nitrate, two parts sugar, and two parts wasabi powder will make an excellent substitute. Cook the sugar and potassium nitrate over a low flame, stirring constantly until it turns into a nice gel-like mixture. Then mix in the wasabi powder until it is well distributed in the gel. Put it into some sort of wooden tube, and cap off the ends. You can put in match-heads as a sort of fuse, but green fireworks cord works great
Using peperspray and teargas could get risky. You will need a respirator. There are some really cheap and nice military surplus gas masks out there, I can recommend the czech m10 m. They are cheap, plentiful, and the filters are easily purchased. There are many other good respirators out there, just make sure your eyes get covered.
Although "antiriot" helmets are widely available, they are not cheap. Motorcycle helmets often provide similar protection at a lower cost. Welding masks can be used, but they are a bit clunky and hard to wear around effectively.
There is a lot of expensive riot armor out there. You really don't need a full suit, try to cover your chest and the arm that is not holding the riotshield. If you need protection for your legs, you can shin and thigh guards pretty cheaply. They will do the job just fine.