Its reasonable to expect double the costs for everything if you add a second bunny. Buying things in bulk with save you some money but youll have to double the amount of veggies and hay (more if you get a bigger bunny). And you have double the risk of emergency vet visits. IMO that is the most expensive thing about having multiple bunnies.
Ditto, what Stickers said. You will need two of everything (cages, water dishes, etc) until you can bond them, which can take anywhere from weeks to months and in some rare cases, certain bunnies can never bond safely. Having 2 separate bunnies takes up a lot of space and is double the work (pen clean-up, out of cage exercise time, etc). Bonding takes a considerable amount of time and dedication.
If you have considered all of this and still think a second bunny is right for you, then it would be best to let Rascal pick his new mate. The bonding process is usually much easier when the bunny picks his friend. Most rescues will do bunny dates.
Do you and Rascal have a good bond? And how much time do you spend with him a day? If you spend a good amount of quality time with him and he gets lots of out-time, he is probably quite content.
Bringing home a second bunny can be a great experience but you have to make certain its the right choice for you both. Carefully weigh out all the pros and cons (for example, what will you do with the new bunny if you cant bond them?)
Hope this was helpful. 