looking to sell/buy camera need advice (read body)

before i start all pricing and stuff is in aud i live in australia

i currently have a canon eos 200d mark ii, and the camera i want is a canon r50. what ive seen is r50 used go for like $700 - 850, while 200d mark ii used go for about $550 - 650. i am willing to put about $300 - 500 maximum into it, if you have any other recomendations for cameras let me know. into since r50 is mirrorless and overall a pretty good camera i want it over my dlsr, i also want better video and better low light shots. thinking about getting a sigma 18-35 f1.8 or something close, but rf mount lense are so expensive. is it worth the switch to mirrorless? also should i get a different camera completely? also have a tamron 16-300 for canon ef which is honestly pretty shit but could probably sell for a bit of money. also have a 67mm polarizer for that lense. thank you for reading if you can please help me out