Hiya
I have had one chinchilla in the past which my sister then took to put in with hers. If you are going to get two I recommend doing it from the beginning, it took my sister 3 months to get these two to go in together! If you get two there is a chance (much like humans) that as they get older they could fight, it is a small risk but one that needs to be taken seriously as you would have to rehome another one, so look at issues of space.
Chinchillas as pets tend to be quite independent and do what they want to do, as a pet they are not normally happy to be held, rather go off exploring what they can see and do! In terms of work and money it would be increased with a second one but wouldn't be doubled as they should share well (fresh and hay) but norma food would be doubled and bedding if cleaning them out more often, in regards to cleaning each animal is different, you will need to see what they are like and how much mess they make and go from there. My sister's one didn't urinate in cage, preferred to do it out of the bars so didn't need cleaning that much! Just a suggestion for the dust bath, when you put it in, leave it for an hour and then take it out, if you leave it in there for longer they will do their business in there! (More chance with two).
Having two chinchillas the work would increase in some ways - petting and trying to get them back in their cage, cleaning and general maintenance but in other ways it would decrease as they would have each other for company and could entertain each other therefore not putting as much stress on you.
Whilst I would always recommend two, consider lastly the life span of a chinchilla, being 20 years if one were to die suddenly would you then introduce another and if so you would always be playing catch up, IYSWIM one will be significantly older than the other and so it continues.
Good luck, they are great pets, let us know what you decide.