Optics are something where you really tend to get what you pay for. I am not sure that any really inexpensive red dot sights are actually a good value. The cheapest sights that I have found satisfactory have been about $100.

Two reasonable and inexpensive small tube style red dot sights are the Primary Arms models and the Bushnell TRS-25. There are many internet threads debating which of these is best, and most such threads are about evenly split on opinions. I have a base model Primary Arms sight that cost about $100. It has a 2 MOA dot and it has proved entirely satisfactory. I have an older TRS-25 that I am not as happy with, but I believe the TRS-25 has been updated, so the older sight may not be a fair comparison. I can recommend the Primary Arms sight, and I can't directly comment on the current versions of the TRS-25.

For a smaller open style red dot, I have been happy with my Burris Fastfire III. However, this sight is closer to $250 with its mount included. Other people may offer suggestions for less expensive open style sights, but I have not personally used any cheaper open style sights that I could recommend. And the Fastfire III has advantages over the Fastfire II that I think are worthwhile.

For somewhat larger sights that are well liked by target shooters, Ultradot makes several models priced from about $150 to $250.

Since I own some of these sights, you may correctly assume that I like red dots sights on pistols. For target style shooting, a red dot is a lot of fun. Unfortunately, cheap is often not really a bargain.

Good luck with your choice.