Building your own homebuilt aircraft means dedicating a huge amount of time, perseverance and resources into your personal project. Do not think that this can be done without too much trouble, it will not. It will take a lot of effort, time and dedication to finish.
Chances are that you will have to spent a considerable amount of time building your dream. And that your project won't live in your living room with you. You will need a place to build and insurance in case something unforeseen should happen while you are not around.
Insurance is important too, especially in aviation as having a small accident can cost into the thousands. We also look at the cost of your project as this will be substantial. Paint jobs aren't cheap, if you want the airplane to look as if it came straight from a showroom.
By all means have your project insured. A special builder insurance doesn't cost that much anually and if anything happens during construction you have got that section covered. Some companies have, if needed, a special financing or loan arrangement, this way you can be sure your project can and will be finished.
When you aircraft is about to fly you can change your policy from build status to flying and be ready and insured when you start taxi trials and even the first flight.
What is it gonna cost me, I hear you ask. Well, kits from Vans Aircraft or Murphy Aircraft can be bought for about 25,000 to 30,000 USD for the average kit they sell. Exceptions like the Murphy Moose (there is even a turbine Moose!) will be some 36,000 USD, but that is a BIG homebuilt.
Pricing will also vary if you go for the quick built, these are higher as the manufacturer has done 49% of the work for you. And all of this is without engine, paint and instruments.
If you go overboard with things like EFIS, HSI and dual COMM / NAV or GPS sets and or autopilots then the price of the instruments can be as high as the kit itself and usually higher. For builders not residing in same the country as the kit manufacturer do count on higher transport, customs and tax fees. These can be as high as 20 to 25% of the kit price depending on your local tax law.
As a safety measure an airplane is usually equipped with navigation (green, red and white) lights and a red beacon and white wing strobe lights. These lights are either the old school light bulbs or the new type LED lights. These LEDs are virtually unbreakable but still somewhat expensive.
Roughly you can divide the total cost to build in three: 1/3 for the kit, 1/3 for the engine and 1/3 for the instruments. Its a ball park figure but for most general aviation kit built aircraft its about right.
When your aircraft finally flies you will need to cover cost for insurance, hangar rental (not if you own a hangar), a new engine and or propeller when its time to replace these and last but not least fuel. Regular maintenance cost will include things like regular inspections, license renewals, oil changes, oil and air filters, tires and other consumables.
The cost you will see when flying is mainly fuel for a large part. Landing fees are common in Europe and can be very high depending which country you fly into. Some controlled airports charge an ATC and passenger tax too.
It would be wise to set up an extra bank account in which you deposit an amount of money for every hour you fly so that when the time comes to spend it on maintenance the funds are there.
Having a credit card is going to help too when making on-line purchases for your aircraft. Make sure that when you are going to do a payment, the site is secure (HTTPS) and verify that you have the correct URL to your bank. Most manufacturers and or parts suppliers accept all major credit cards. Payment by bank transfer can be done too, make sure to obtain all bank information, SWIFT/IBAN codes, bank name and address and account details. Sometimes bank transfers are cheaper than credit card transactions.