The Allen amps, whether in kit form or pre-built, are of truly outstanding quality. Great designs and top-shelf components all the way through. But as you've noticed, they AIN'T CHEAP. Also, unless you are very confident in your soldering skills and have built an amp or two previously, I wouldn't recommend the kits, as these are most definitely NOT novice-level builds. Now, if you're ready to drop $1900 plus shipping on a pre-built 2x10 Brown Sugar, I'm sure you wouldn't be disappointed. But that's about $450 more than a '59 Bassman RI will run you, so you'll have decide if it's worth the upcharge to you.
Another amp that you might want to consider is the
Fender '68 Custom Vibrolux Reverb, part of the '68 Custom amp series that came out in 2014. I've read nothing but excellent reviews on these amps. I remember Joe Bonamassa commenting that "Fender really got it right" with these amps, and he's a very tough man to please. He even included the smaller Deluxe model as one of his
"5 Most Underrated Amps" in an article on PremierGuitar.com. The Vibrolux model is 35W with 2x10" Celestions. It's a two channel amp, with one "vintage" channel staying true to the classic silverface Fender tone (including reverb and tremolo) and a "custom" channel with a Bassman tone stack, giving more mids & bottom end and a bit earlier break-up. Very nice sounding amp, and very flexible. As usual, there are several demos on YouTube that you can check out. And I would expect that most decent-sized music stores would have one in stock that you could test drive.
P.S. Just started a new amp build project. I picked up a
BYOC Brit 45 head kit (Marshall JTM45 "Bluesbreaker" clone) and am modifying it to JTM50 specs--think 50W Plexi with a tube rectifier. The two circuits are very similar, with the major difference being that I'm installing EL34s instead of the KT66s in the JTM45, and am using a 50W Plexi output transformer to match up the primary's impedance with that tube type. The other major modification is the installation of a variable voltage regulator (VVR) in the power supply stage that allows you to dial down the final output while still keeping the amp "cranked" for that sweet Marshall crunch. Similar idea to using an attenuator, but by reducing the voltage supplied to the amp circuitry rather than attenuating the output with a resistive or reactive load, and thereby results in less tonal change.