Hi, I work at Casa Sanchez so hopefully I can give the right answers. I shall try not to advertise, but there is an ad on DR1 in any case. The rates start at US$79 per night, plus tax, which brings the lowest rate to US$ 100. This includes breakfast, use of the gym, free WiFi, free water. If you are seeing a US$ 130 rate, this is probably because the hotel is busy and we don't have the cheapest rooms available. The suites are like apartments inside a hotel, and the cost is US$130 a night plus tax. If you go to the website - follow the link on the ad in the DR1 listings, often it comes up on the home page - you can then send a message and for a longer stay, we will do deals on rates.
Like anywhere else, you're going to get what you pay for. Casa Sanchez has an amazing reputation, check it on Tripadvisor. But it pays the staff above the normal salary (double or triple in some cases) and provides a lot of extras - the breakfast is really nice for example, and the gym is big and free. Casa Sanchez is about the same price as the other nice boutique hotels - Villa Colonial, Beaterio, Palacio.
Regarding overnight guests, Casa Sanchez does NOT allow anyone to bring in overnight guests, so no bugarrones and no chicas. If you arrive and check in on your own, nobody is allowed to join you. All of the nicer hotels have the same policy. Why? Firstly for your safety, it is extremely dangerous to bring prostitutes back to your room (and yes folks they are prostitutes), you have all your belongings and your money and your passport there. Secondly because those kind of people often bring other problems - taxi drivers demanding money, police demanding money - and the hotels don't want the hassle. We always recommend that if you meet someone, you take them to a cheap hotel and leave your belongings in your room. The person will also not know where you are staying, so won't keep coming back and hassling you. You can get a cheap hotel for a couple of hours for US$ 10.
If you want a cheaper hotel, I would suggest Adams Suites. It is very well run, and Gilbert provides excellent service. The downside is noise, it's right opposite the gay clubs and the street gets very busy and noisy after midnight on Friday, Saturday and Sunday, and this goes on until 5am. So it's hard to sleep. And secondly no pool. I think, but I'm not sure, that Gilbert allows you to bring overnight guests back, but he will definitely help with this if you email him.
I would avoid Duque just because of the location. It's on Independencia, so it's a little walk from the Colonial Zone, but this is in the dark and on a street where you could be mugged easily, very few police.