I've done ~15 events over the last 5+ years as pure one-man shows, the only help has been that I've usually shanghaied one or two of those who turn up very early and used them to help me setup the tent.
We use http://brikkesys.no/
, a custom program that uses two EMIT registration units: The first is used to register participants (no pre-registration) so that any returning competitor can be handled with zero typing. The other unit is a clock unit with attached split time printer which is used to handle finishers. The combination gives a running total of total registrants as well as how many are still out.
I normally hand out maps while people register, can tell them to keep it folded until they start or I'll just leave map boxes at the start point.
Payment is always handled on the honor principle, i.e. I just leave an open cash box and tell them to do it themselves. Lately I can also receive electronic transfers via Norwegian cell phones. BTW, over more than 10 years (since I started doing this as a more or less one-person event) that open cash box has always been slightly overfilled by people who skipped getting change except for one single event where two people forgot to pay, so the average is solidly positive.
Over those same 10+ years I have had one missing runner, a lady who knew very well that (a) I was alone, (b) she had passed the final cutoff time, (c) the finish was less than a km away, so after 30 min with no sign of any left-behind gear or anything I decided that she had most probably just forgotten to check in after finishing (something which does happen sometimes). I think I tried to call her but then I decided to go out and collect the controls with the idea that if she was still out there I would probably find her.
While I did that she did return and was extremely angry (in emails) afterwards that I had packed up and left before she came back. "It was her right to stay out on the course as long as she wanted, disregarding any cutoff times, and my responsibility to wait for her however long it took."
She has not been back since then fortunately. :-)