Answer. The expensive bettas are mainly the quality selective bred ones with beautiful finnage, perfect colour rays and tail shapes. Suitable to be show bettas I suppose.

Define those RM7 ones, what are they? I'm quite curious to know the fin type and colour variation of them. It's an odd pricing though. The LFS I've been to mainly sells the bettas at RM2 or RM10. Were you referring to the RM7 ones or the RM40-50-70 ones that you like?

Besides that, if you say shrimp and if I'm not mistaken that these shrimps are those RM1 for a pack to use as bait for fishing, then I wouldn't recommend to keep the bettas with them. I've once tried this in my female bettas tank and they've eaten all of the shrimps by the next day.

Further, if those shrimps are the very pricey pet shrimps, i.e: cherry shrimp, crystal red shrimp; you should better not keep them with the bettas for what it may be almost the most expensive food for them.