You CAN find Denebs here and on AmiBay and for less than $600 USD. I recently got 2 on AmiBay and 1 here for a low of €350 and a high of €450 or $400 - $500 USD. Watch for 4000 systems for sale that have some expansion cards. I've gotten 2 that had a Deneb in them. It can cost more to buy a whole system but the cost of the individual components is cheaper than buying separately. Of course, that's only a good idea if you have a use for many of the components or think you can sell them for a good price and recoup the costs.
The X-Surf and RapidRoad works, it works very well. In many cases, though, I prefer the Deneb because it supports DMA (with the right revision Buster and Deneb firmware) but the best feature is the 4MB flash RAM on it. 2MB has the Poseidon USB stack installed. The other 2MB you can install other things like libraries. For the machines that I haven't installed 3.9 Kickstarts in yet, I have all of the 3.9 (and other patched / updated modules) in the Deneb's flash RAM which lets me boot to AmigaOS 3.9 without any resets which greatly reduces boot up time. You can also install the files needed so that Poseidon is active / available at boot up so you can use USB devices like keyboards and mice at boot up. It also lets you boot from a USB flash drive or hard drive.
It doesn't hurt that the Deneb is fast as heck. I've got one machine booting from a high speed thumb drive and file access is amazingly fast - windows (even un-snapshotted ones) open instantly. It's a convenient and fast way to experiment with different configurations.
The Deneb can be (usually is) expensive but it can be worth every penny IMO.