Usually hotels are considered quite safe as the owners will employ guards. However, don't be complacent and make sure that you are aware of your security also in the hotels. Be prepared to pay your entire bill in cash USD.
Prices for hotel are overpriced in the Monrovia area. It ranges from USD50 per night at Crown Hotel opposite the Paynesville City Hall - USD350 per night at Mamba Point Hotel - near the American Embassy with many others priced at the high end in between.
There are also a number of guest houses and furnished apartments available especially in the Mamba Point and Sinkor areas.