If thinking of a "4300.00" compressor do research!
Some people have had luck, some have gotten nothing from different vender(s).
Some models work well after MUCh work , machining included.
Personally I would love to have a tiny ( dry ) air compressor that just filled my rifles,or a tank, suits my needs right now.
The altros "booster" - yes you need a shop compressor -
http://www.airgunnation.com/topic/altaros-booster-arrived/ Total cost of booster and scba tank & fittings and shop compressor ( which I needed anyway) was under , gulp, $1,000 but a LOT better than NO air.
PA seems out of stock on both their booster & smallest compressor right now.
Have you check Nitrogen yet?
Some places in the U.S. it can be rather inexpensive ( I know of one person in TN who get's the huge 400lb size tank at $80.00 per year , most places seem more ?).
John