Adding sand later will be a pain, but it IS doable if you're so strapped that you can't afford proper sand now.
If I had to choose between CC and BB to start my tank off with the expectation that down the road I'd change over to sand... I'd start out bare bottom. I'd rather not have the toxic waste dump sitting there that is bound to release toxins upon removal later. Is it better to add the sand now? Yes. In an ideal world you'd certainly add the sand NOW. I always have,but I have added more sand later and with the exception of the sand storm, there hasn't been any ill effect. Is it better to add CC now and change to sand later? No. If that HAS to be the case, I'd start out bare bottom.
MOST fish don't need sand. You'll have to check with your stocking list to see which of them like to burrow. Those will not be particularly pleased with a bare bottom tank. The rest won't care.
You can start the tank with 80% base rock (cheap) and 20% live rock, 1 bag of dry sand from the LFS (optional based on your thoughts from the previous paragraph), some power heads and a coctail shrimp. Everything else can come after the cycle. You can even plan for a sump and add it later on!
You don't need a skimmer to cycle. Truth be told? You really don't NEED RO/DI, especially if you're going to do a major water change (75-80%) at the end of your cycle to remove the nitrates. You can start with the RO/DI then.
Just my opinions, of course! In an ideal world, you'd wait until you had everything in order. If you're insisting on getting started ill prepared, best not to waste money on items that you'll want to throw at the wall later on! That will just drive your $/gal up to 60-70! Who needs to do that?!
