At that pricepoint, it's probably going to be a case of pick 3 out of 4.
TG + RGB fans add to the price, and, with modern trends pushing to closed off front panels, "good airflow" is probably going to be sacrificed to hit the other options...
Enso Mesh - TG, RGB (2 fans included, just the one RGB fan + strips), ATX support. Pretty poor airflow.
https://uk.pcpartpicker.com/product...black-atx-mid-tower-case-bfc-esm-150-kkwgk-rp
https://www.tomshardware.com/reviews/bitfenix-enso-mesh-mid-tower-atx-case,6007-3.html
Masterbox Pro5 RGB. TG, RGB (3x RGB fans), ATX support. Same, pretty poor airflow.
https://uk.pcpartpicker.com/product...pro-5-rgb-atx-mid-tower-case-mcy-b5p2-kwgn-01
I would consider looking at more budget-oriented TG case, and add RGB fans yourself.
Perhaps the Phanteks Eclipse P300 TG?
https://uk.pcpartpicker.com/product...mpered-glass-atx-mid-tower-case-ph-ec300ptgbk
https://www.tomshardware.com/reviews/phanteks-eclipse-p300-case,5244-4.html
Paired with, maybe MasterFan Pro 140 Air Pressure RGB's?
PCPartPicker part list /
Price breakdown by merchant
Case: Phanteks - Eclipse P300 Tempered Glass (Black) ATX Mid Tower Case (£49.97 @ Laptops Direct)
Case Fan: Cooler Master - MasterFan Pro 140 Air Pressure RGB 46.2 CFM 140mm Fan (£15.18 @ Amazon UK)
Case Fan: Cooler Master - MasterFan Pro 140 Air Pressure RGB 46.2 CFM 140mm Fan (£15.18 @ Amazon UK)
Total: £80.33
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2019-04-24 19:24 BST+0100