Much of a professional's or a firm's fee is based on their reputation, degree of professionalism, experience and skill. In this case, offering service in English is a value added service that is important to some clients. The law firm you have approached seems to be ranked closer to the top of the list than the bottom so it is not unreasonable to expect their services to be priced higher than smaller or lesser known firms or individuals.
Be sure you understand what you are getting for your money. I suspect, that any problems with the title that need to be resolved or further investigated will cause the final bill to go up, potentially a lot depending on the circumstances. That would be a good point to clarify with them. Get and keep everything in writing. No verbal commitments.
You can choose to buy a Rembrandt, you can get a paint-by-numbers kit or you can buy the kit and have someone else apply the paint. You not being in the DR may add to the potential for costs to go up because of administrative overhead. At least with Guzman, if you feel dissatisfied, you can come back to DR1 and perhaps receive a measure of redress as they advertise on this site and maintain a presence in the Legal Forum.
That knife cuts both ways. I'm sure they can and probably will read this thread. Personally, I don't find $100 to have an educated professional perform a title search to be unreasonable. Is that amount higher than Juan with the office above the colmado, maybe but at least with Guzman, you can expect your emails to be answered once you pay the retainer and they can provide service in English. Two rather important points for an anglophone outside the DR.
Good luck.
