Upvote:2
Although not in the Schengen area, Bulgaria would like to be, and as part of their application process is applying Schengen rules as though already a signatory to the Schengen agreement. Since about 99% of the rules that are of general interest are applied in the same way by every Schengen member it is fairly safe to assume that whatever of a routine nature is the case for a Schengen country, for example the types of visas and in particular the 90-180-visa-rules (see Usage guide) and the Short-stay Visa Calculator (for details), is applicable.
Upvote:3
No, you don't need visa for a short-term visit to Bulgaria with Netherlands residence permit. According to Timatic:
The following are exempt from holding a visa:
Passengers with a residence permit issued by Netherlands for a maximum stay of 90 days.
The maximum stay is granted within 180 days.
Passengers with a D visa issued by Netherlands for a maximum stay of 90 days.
The maximum stay is granted within 180 days.
Additional information:
Visitors are required to hold proof of sufficient funds to cover their stay and documents required for their next destination.
However it is suggested to check the visa requirements before booking tickets, unless they're refundable, as the airline will not refund you on the grounds of not having a visa.