Our babies are 18 months and a day apart. At the beginning of my pregnancy I was pretty panicked at the thought of another so soon. But, now the baby is 8 months old, our first daughter can't remember not having a baby around, the baby gets the biggest smiles whenever she sees/hears her big sister and we really can't imagine not being a family of four.
It is tough though. Your toddler is going to have a lot of energy and sometimes it's hard to feel like you can keep up. I found that I had more energy after the baby arrived than I had when I was pregnant. So keep that in mind.
Some things that have helped us:
1. A routine or a schedule or something to give you something to look forward to throughout the day. I could pretty much count on the infant BFing every 3 hours or so during the day - I could plan then for an activity to distract my toddler so she wouldn't be crawling all over us.
2. High chairs, Playpens, books, short online kids shows, etc. When you need both hands for the baby, these keep the older one occupied/contained for short periods of time. There are times when my oldest actually asks for a "time-out" just to get a break and be alone. She is much more calm and collected afterwards.
3. You'll be tired. It's ok to take naps. Encourage naps for everyone- you included! Pick a book that fits your parenting style/theories that will help you help your kids to sleep. It has made all the difference to us.
4. Winter is tough. Tough to be inside so long. Tough to get out in the cold with TWO little ones. Don't be afraid to send the oldest over to a friends house to get a break. It's nice for toddlers to socialize. Also nice for mommies to socialize too, so maybe go along as well.
5. Play as a family. Let some things go every once in a while. when you let yourself focus on enjoying the children it really does make everything better. Go to the park, even on hard days. My husband really enjoys chasing/rough-housing/wrestling/tickling the kids and they love it too.
There's so much more, and the day-to-day does get tough, but you can do it. There's a reason there's a 9-month waiting period before babies come - to help us get used to the idea, and have some time to prepare.
Sorry this is getting so long - but as far as the money goes, you already probably have all your baby stuff. #2 does not really require a lot, especially if they are the same sex. But grandparents love to give presents, consignment shops often have new/barely worn baby clothes (they really don't get used all that much). And -shameless plug- cloth diapers, I found, were easier to use during those early months when you're changing so often. And they prevented all those severe blow-outs, so fewer stains on baby clothes and they actually ended up needed fewer clothes in all.
Best of luck. I hope your pregnancy goes well. It really is a joy to get to know your newest family member. Coming from a large family of 6 myself, I am best friends with my sister who was closest in age. And they are little for only a short time.
-K.