Depends where you live, cannot work out from your title.....I can on,y assume somewhere illegal to own rays therefore warm climate. 2 main costs to rays....feeding them (costs a lot for quality) and hearing the water, if in hot climate then not an issue.
Rays are not cheap, they need good filtration which means good pumps running 100-200 watts and then good quality diet. Bds may cost a few thousand but that's a one off.
Please do not talk about sponge filters, you need to read up on what these guys need. The filters need to be the best you can buy.