I don't know of even a Bottlehead kit that falls in your price range. While SET amps are "simple" in design, they are never really that cheap to make, primarily because SET topology puts extreme demands on the output transformer. The transformer is a very expensive part.
Is there a reason you mentioned the 2a3 tube? Of the three most common directly heated triodes (2a3, 45 and 300B) used in SET amps, I think the 2a3 is the leanest sounding (tight, but thin sounding upper bass) and would not be my choice for "sweet" and "easy to listen to." What I like about the 2a3 is its clarity and wide open top end. I like the sound of 2a3s (my main amp is a parallel 2a3 SET, but, it would not be my choice in a lean sounding system. The 300B is probably the warmest of the three types I mentioned, and has the highest output, but the tube itself can be pretty expensive. I really like the sound of 45 tubes (tight, but fuller bass than the 2a3, not as rich in the lower midrange as the 300B), but they have the lowest output of the three. Higher powered directly heated triodes include the 845 and 211 tubes, but with these, the tubes are expensive and the higher voltage power supply means more expensive parts and more care is needed in construction (potentially fatal voltages involved).
I have heard the Bottlehead monobloc 300B amp. It is a decent amp, not too expensive, and easy to build, but, I think it is more than double the price range you mentioned.
Is there a reason you mentioned the 2a3 tube? Of the three most common directly heated triodes (2a3, 45 and 300B) used in SET amps, I think the 2a3 is the leanest sounding (tight, but thin sounding upper bass) and would not be my choice for "sweet" and "easy to listen to." What I like about the 2a3 is its clarity and wide open top end. I like the sound of 2a3s (my main amp is a parallel 2a3 SET, but, it would not be my choice in a lean sounding system. The 300B is probably the warmest of the three types I mentioned, and has the highest output, but the tube itself can be pretty expensive. I really like the sound of 45 tubes (tight, but fuller bass than the 2a3, not as rich in the lower midrange as the 300B), but they have the lowest output of the three. Higher powered directly heated triodes include the 845 and 211 tubes, but with these, the tubes are expensive and the higher voltage power supply means more expensive parts and more care is needed in construction (potentially fatal voltages involved).
I have heard the Bottlehead monobloc 300B amp. It is a decent amp, not too expensive, and easy to build, but, I think it is more than double the price range you mentioned.