Fish owning is a learning process :)
My personal suggestions would probably echo what's already been said and at the risk that I'm repeating someone - sorry! I don't feel like reading everything. X)
Research is one thing. Actually doing it is a completely different proposition. What worked for one person may not work for you. You should always be ready in the event that something doesn't work out to have a back up plan. :)
The cheapest and most economical/fish friendly solution imo would be to split a 10 gallon like several people have said. You can split them up to 4 ways and still have good space for everyone and only have to pay for one filter. Depending on how prepared you are and how far you want to go, this can end up being a very costly plan.
You can make dividers out of mesh from craft stores as long as you reinforce them. Petsmart also sells dividers that are premade but you have to put them together. I also had to cut them down to size so they'd fit. Petsmart's dividers are also fairly transparent and your fish will be able to see each other which could douse them with undue stress. Mine seem to get along just fine and only occasionally catch a glimpse of each other through the mesh and the plants that line their segments.
Live plants look fantastic but be prepared to stay on your toes should you choose to have them in your tanks. Many of them have different needs. The easiest by far for me has been java ferns. They grow like weeds and take just about any lighting situation as long as there is infact light. Live plants can also be cheaper than silk plants and benefit your fishies greatly.
If you don't have time/want to wait for a tank to fully cycle, seachem stability has been AMAZING for me. It's a bit pricey, but seachem's whole line is top notch. I swear by it.
How to save money doing this:
- Check good will, pawn shops and wal-mart
for tanks and supplies. A 10 gallon at wal-mart is $12.97 for the tank alone. A full set up with a hood and filter will run anywhere from $20-50. I really, really, really don't recommend wal-mart gravel though. Or wal-mart fish for that matter.
- Ebay has been a god-send
for me. I got a heater off of there for a 10 gallon for $8, shipping included. It took me a couple weeks to get it but saved big bucks on a thermostat heater. If you need a quick fix, heaters in pet stores are $15 and up for a 10 gal.
- Live plants, I've found, are cheapest at Petco
here. Definitely look around before you buy and bring a coupon. Petsmart current has a 15% off coupon floating around if you bother to print it out. Good stuff.
- Every betta should have a cave
or somewhere to hide in -- and a cheap $1 clay pot can suffice well! Petsmart has the best variety of natural looking (or otherwise) decor that can serve as caves, imo. And they're not unreasonably priced. They have the best sales..
- If you have a local fish store that's mom-n-pop style, definitely check them! You might be surprised by their prices, pleasantly. And they'll often haggle.
I'm always on DA if you need me or just want info. I've learned as I've gone, too. And I learned the hard way in some cases. :P
PS - Petsmart and petco often have coupons on the door to the freezer with their frozen food. Definitely ask if you don't see it! It can be a dollar or more off.