Two rabbits are generally not more expensive than one. Pellets, hay, fresh fruits and vegetables, and litter-shopping for two puts little additional strain on the budget. The exception is medical care. The introduction can be as dramatically hostile as the marriage is devoted. Wild rabbits do not initially welcome strangers with friendly greetings but rather defend the warren against any newcomers.
Introductions are often difficult for the supervising human.
I have attended many introductions over the years, and only the firsthand observation of the happy, peaceful outcome of these skirmishes has reduced the stress level for me. This shows in detail the process by which rabbits who start out as implacable enemies are transformed into inseparable friends. Bereaved rabbits often accept a new friend more readily than a rabbit who has never had a partner, a tribute to both the resilience and the sociability of rabbits. However, you may wish to spare your rabbit the heartache, and the illness that sometimes accompanies it, by introducing a third rabbit to your pair. This is a primary reason for having a threesome, but there are other benefits for you and for the rabbits.