Disclaimer: I have engaged in this role many, many times so my comments are a bit biased toward what I have experienced as working.
First, Bus Dev has many shapes as defined by the employer/client using them. To some Bus Dev IS Sales, to some Bus Dev is pre-sales, to some Bus Dev is the hunter role while Sales is the gatherer role, to some Bus Dev is about finding strategic partners/channels so that the sales ramp can be compressed...and it goes on. I have seen it defined differently by industrial sector and even within companies in the same sector - no one size fits all.
So preferably first define the objective so your discussions are on point. You don't want to waste your time or the BD resource's time trying to find out where/how the time spent will make the most impact. You should know where you are needing the help and focus like a laser on that area. A solid BD resource should be able to help in many ways but there should be a focus.
Secondly understand BD gurus, like Sales execs, have spent a long time, perhaps decades building not only the rolodex but the ability to find the right person to talk to, in a way that creates an opening for your product or service.
Thirdly, most BD resources won't work for 100% commission as it places all the risk on their side of the table. There are always exceptions but I personally have not seen many, if any,.
However, BD resources may be open to a shared risk scenario with a startup, depending on what stage the business is in, what the product acceptance has been so far, sales trajectory rates, customer churn rates, close rates, etc. He/she is looking for some proof that taking some risk on their side is worth it.
In terms of getting someone on board, be creative in what you offer:
b) compensation accelerator's tied to results
c) ability to work from home
d) part-time so that he/she can continue to diversify their efforts; if a 100% of time is spent on your product and it fails the resource has to go back out and build business from scratch
e) potentially benefits
f) and last but not least to be involved with a cool sexy product that no one does like you do!
Ok, done..let me know if you need anything else..