Microneedling is relatively safe especially if not done too deep (DIY or salons usually do not offer very deep depths). It is a simple procedure, so salons that are more reputable should have their staff trained properly for this procedure if they offer it.
Simply needling the scars will have very little results for most sunken scars though. Some doctors use microneedling RF that creates coagulation zones with microneedles to achieve better results. I use such a device in my clinic as well, but even my gentlest resurfacing laser achieves more result than the microneedle RF device - proven with clinical studies. Microneedling without RF would be even less useful than that.
If you are on a budget, you may end up wasting more money on a procedure that has little benefit compared to spending on proper medical procedures instead. You can always submit a treatment quote here to find out the prices of different procedures and clinics.
Hope this helps!
