I can’t speak for German prices, but I can give you some UK prices and ideas as an example. (Source: Sound-Engineer by Trade in my previous life.)
Decent/Affordable sounds don’t usually belong in the same sentence unfortunately. You can often get good results by munging stuff together from the likes of freesound.org and similar websites, but usually they are in terrible formats and have a lot of background noise, and there are very limited options. They are also free, so nearly everybody else is using them. The Marketplace does have some SFX packs on it I believe, all of which so far sound up-to-scratch but they are a tad pricey for hobby development.
To record (decent) audio you need three things: A Microphone (minimum of £100 spend), an Audio Interface (something like this) and a DAW (Digital Audio Workstation). Reaper is a great DAW (why people still use Audacity over Reaper I’ll never know), and for commercial usage it’s incredibly cheap. There are also a huge variety of plug-ins available for it, since it supports the VST Plug-in format. While you can use a regular PC microphone that plugs into the Mic input on your motherboard, don’t expect decent results with it. Good sound is all in the Microphone and the Pre-Amp, and no matter how expensive your motherboard, I can garauntee you the onboard sound will always be terrible.
That should answer questions 1, 2 & 3. Voice-Over equipment comes in the same form as your Microphone you bought for recording sounds. Popular choices are the Shure SM58, Shure SM57, SE 2200A or similar. Dynamic Microphones are best for loud noises, whereas Condenser Microphones tend to capture more high-frequency detail, but are less robust. Don’t let anybody sell you a Microphone cradle, those things are bloody stupid. Just buy a regular microphone stand and you’ll be away
As for voice actors, that really depends on how good they are. Experienced VO actors would probably charge between £200-500 per session, but honestly you’ll be surprised how well your friends can do the job if you pay them with a beer or two! Some tips for VO recording:
- Give them Headphones so they can hear how they actually sound. Sometimes applying a touch of reverb on the headphone mix can make them feel more comfortable.
- Never tell the person your recording that they suck. Stage fright and paranoia will ruin it both for you and them.
- Record at least 5 takes of everything and pick the best one.
- Put them in an isolated room, and add the effects that you think you need afterwards. Try to eliminate as much background noise as possible.
Hope this all helps
(PS, Focusrite, Presonus, Avid, M-Audio and Alesis make fairly decent Audio Interfaces for low-cost)