Yep true, unfortunately nothings is cheap in this hobby £100 + for a hang on refugium
But IMOH i think it’s got to be the easiest and safest solution for you and when you think about it, its probably the cheaper option as well , you would be looking at £40-£50 for a over flow box and £70+ for the return pump from the sump + a light if you decided to grow macro algae. So when you look at it like that i guess it’s not so bad