Over the years the community as a whole has mostly destroyed all the components of these engines bit by bit with big single turbo and drift builds. As a result there is very little good quality usable stuff floating around at this point from which to put together blocks. At the time of this writing I have only a handful of components on hand, not enough to pre-built engines and send them out the door in this manner, only enough to replace 1 or 2 parts in a customer's core I may be rebuilding.
At this point you are pretty much down to having to buy new components one by one from mazda as needed, or spend the ~$6000 for one of those "all new parts" engine blocks that mazda periodically makes available for the REW/FD application (note that as of this writing, these are not available for other applications to my knowledge).
IF you buy the setup listed on my site, there is no core charge.
The topic of core return/exchange really only works for local/regional owners able to deliver their core in person to me in east TN.
Core value is determined based on what inside is still reusable, which cant be known without teardown and inspection. I can't negotiate for a core blindly and pay up front without knowing what's inside it, if it turns out to be a boat anchor then that's just money I tossed out the window.
Truck freight shipping, even at minimum for nearby/regional customers, costs the same as the value of a decent condition core (depending on year/model), say 3-500 bucks. I can't pay for both the shipping and the value of the core that the owner wants to sell me, so thats why it only works out for those who can deliver and wait while I tear down.
That's why I omit the entire discussion for pre-built engines listed on the website.
At this point I do not require deposits to begin work on standard rx7 rebuild jobs. I bill the entire balance at the end of the job. If you are asking for expensive new parts or custom services that I have to pay out of pocket for up front, then I may ask for a deposit up front.
Regarding deposits to secure an appointment in the future:
I work from home as a one man operation. Sometimes I have to run errands, parking and storage space are also very limited. For these reasons, all visits are by appointment, to let me regulate how much work comes in and when, and be sure that I have given the owner all relevant information before taking their job.
Due to fast-changing owner plans (some owners change their mind in less than a week, some do it multiple times) I do not make future appointments farther than about 48 hours ahead. This reduces the time that owners can waffle and also allows me to prioritize response to owners who are ready to move forward immediately over those who might come next week or next month.
I do not take deposits to hold spots or book future appointments. Deposits are well and fine but in order for a deposit to serve it's true purpose it has to be a non refundable deposit in the event the owner backs out leaving me without work that week, and there's no way to do an electronic funds transfer that can't be eventually reversed or charged back. Cash or USPS money order are the only truly non-reversible payment methods, and virtually no buyers can be bothered to tender deposits via those methods which makes the entire concept moot. So it's a conversation I avoid altogether; I have enough on my mind trying to run all aspects of the business already, I simply want to have the jobs show up and do them in the order they arrived, without the need for more administration or thought on my part.