In
this tread you can find many tips in getting money fast.
Best option is available if you have WA. First thing you should do is go to china, pick books from bookshelf in Base camp, when you get home you can sell them for 20-25 000 $. Also, collecting and adventuring/tomb raiding can help getting money fast.
If you find tiberium in Relic store or consingment store, buy it even if you're short with money, sent it to cut, and let it grow. It is worth it.
Sims employed in Architecture Profession get nice discount on everything in build/buy mode. It is worth to employ your Sim just before you start building and let them quit after that if you don't want to play it.
Photography is another fast money maker, you need around 5k to spend on expencive camera and photos while you skill up, in 2 days you can max that skill, get 75 different photos and make more than 10 000$ per day just around Sunset Valey.
Your Sim don't need to be elated all the time, but you can easily get few nice mood buffs - expencive bed that is first thing to purchase give you comfy moodlet, nicely decorated and eventually Good night sleep moodlet. There is also fun/having a blast which is easy to accomplish. Make a routine to for example after getting up, eat something (rather fruits from inventory then bad food from cheap stove and fridge), use toiled and shower and go to skill up with fun raising activity, or at least not stressing activity. There are many tricks with different traits to use, from neurotic to eco friendly trait.
You can use free floors and wall papers (recolor them to look nicer) to save money, don't use windows if you don't have beautiful vista and you don't need only one smallest window to enjoy beautiful vista moodlet. Beautifully decorated can be achieved with butterflies and bugs, specially the rare ones (if you know where to find them it is not too time consuming).
I never start with premade homes cause they have tons of not necessary objects and cheap furniture. You really don't need TV or a dresser.
You can always move in some of the rich townies.