plenty of cheaply priced hotels in both areas. I generally stay at the Mystik in SD, $45 to $55 and the El Caucho, $25 to $35 in BC. Mystik---809-686-3627, El Caucho---809-523-6734.
Please be careful. I suggest that you use posted recommendation rather than Internet based advertising. And/or contract the selected hotel directly. In Boca Chica the Milanello shut down in late 2006.
To get this back in business, one would have to bull doze it flat and start again.
Check out kakay.com. I've booked with them often and without any trouble! I stayed at the Hodelpa Caribe Colonial, right in the heart of Colonial Zone, SD, and it was nice! Breakfast and wi-fi included, and the room wasn't bad...just a tiny little place but very good price!