Rats need to be in pairs. My last rat was a lone rat. I did eventually get a friend for him after he spent 1 and a half years on his own. He refused to be paired with the new rat and was seriously agressive. I worked for months trying to intro them in many different ways and it failed. I personally think that if he was introduced to another rat when he was younger, then it all would have been fine. I didn't know better at the time and it was totally my fault. Saying you can give a rat enough socialising and attention is really wrong. If you have a lone rat they require a LOT of attention, and i found my lone rat to need too much attention - and i didn't have enough hours in the day to give him all the attention he required.
I ended up with two rats, in two seperate cages, which became more hassle than i needed at the time. When my lone rat passed, i got a baby friend for the now elderly rat that was originally the 'friend' for the lone rat. The baby rat has bullied him, and they aren't living together. The few months they spent together before my little guy got a bit over hormonal - was amazing. Its amazing to see two rats living together, sleeping together, playing and grooming.
Now i have an old guy living in a cat box, who has free-roam all day.. and a baby rat in a massive cage on his own. My older guy is perfectly happy on his own. He isn't a social rat, and never really has been. But, I would NEVER dream of leaving the baby rat in there on his own. He is miserable, won't sleep in his hammocks anymore, pines for attention from anyone walking past, grooms me frantically when i put my hand in the cage. I'm unemployed, but the difference in food and cat litter etc. isnt that much different for having two. I will be getting another baby, or possibly two to house with my baby boy in the very near future.
I think, if you can't afford to look after an animal properly then you shouldn't at all. And, you should do thorough and proper research before you bring any animal home, and also think of the future and possible circumstances (financial etc.), because if you take an animal on your in it for the long run (imo)