TL;DR: This is a merge of the SR3 system and the SR4 system. It might be interesting. It might also be a little rough around the edges, but I think it covers the basic ground. It's probably about as quick in play as doing those decreasing dice pool summations.
I've come up with a house rule:
Availability and normal Interval time (for a piece of gear, based on its cost) factor into acquiring gear.
Multiply the Interval by the ( Availability x (1/4) ) for Legal items, ( Availability x (1/2) ) for Restricted items, or ( Availability x 1 ) for Forbidden items. This gives you the Base Acquisition Time of an item.
The player then rolls his Charisma + Etiquette (relevant specialization most often Street, could vary), and divides the Base Acquisition Time by the number of hits. This is how long it will take to acquire the item.
If the player wishes to use the full resources of a contact, he may add that contact's Connection rating in dice to the roll, but must pay (5 x Connection rating)% of the item's cost as a "finder's fee" to the contact. The contact cannot be used again in this way until the acquisition is complete or abandoned. Beyond that, a character may increase the base price of the item by 25% to gain an additional die. This may be done up to 10 times (250% increase for 10 dice).
If the player wishes to reduce the cost of the item, he may do so by being patient. He may reduce the base cost of the item by 5% by adding one extra Interval to the base acquisition time. This may be done up to 10 times, or up to a 50% reduction in cost. This may not be combined with increasing the base price for extra dice, but it may be combined with using a contact's Connection rating as a bonus.
Once the acquisition time is determined, halfway through that period the player must negotiate the final price of the item. Take the modified base price of the item and then apply cost adjustments as listed in Street Costs. Then have the player and the seller roll an opposed Charisma + Negotiation (Bargaining) test. Each net hit provides a 5% cost adjustment in favor of the winner of the contest. At the end of the acquisition time, the player meets with the seller and exchanges that amount of money for the item(s).
The player is allowed to arrange multiply buys in the same time period, but doing so might put him in the position of having to blow off one meeting to attend another, which could make sellers understandably upset, especially regarding high-risk illegal items. Do so with caution.
If the player fails the first roll completely (0 hits), he may try again, but increase the cost by 10% and double the interval.
If the roll results in a glitch or critical glitch, something goes wrong during the process. On the initial Etiquette roll, a player has stumbled across a sting operation, a meeting is accidentally set in the middle of a gang war, or some other negative circumstance at the GM's discretion. On the negotiation roll, a glitch or critical glitch could spook the seller into abandoning the meeting, or his bodyguards could get twitchy and start shooting. Again, GM's discretion.
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That's a little bit wordy, but what it comes down to is a couple simple calculations and two dice rolls. Examples, using a negotiator with 10 dice and a seller with 8 dice (and a dice roller):
Rating 3 Micro-Transceiver: Availability 6, Cost 600
-- base acquisition time: 36 hours (1 day 12 hours, or 6/4 days)
Initial roll: 3 hits.
Acquisition time: 12 hours
Negotiator: 3 hits. Seller: 3 hits.
Street Value: Stolen (-20%)
Final cost: 480
Combat Axe: Availability 8R, Cost 600
-- base acquisition time: 4 days
Initial roll: 4 hits.
Acquisition time: 1 day
Negotiator: 2 hits. Seller: 5 hits.
Final cost: 690
Ares Alpha: Availability 12F, Cost 1700
-- base acquisition time: 24 days
Initial roll, using Cxn 3 contact and paying +50% for 2 extra dice (15 dice total): 6 hits
Modified base cost (+40%): 2380
Acquisition time: 4 days
Negotiator: 3 hits. Seller: 2 hits.
Final Cost: 2261
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The pros:
1) I can hack out those acquisition times and modified costs in less time than it takes my marathon dice roller to go through his dice rituals.
2) Everyone likes a straight-up Opposed Contest, because it involves Winning rather than Grinding. It's more exciting.
3) Obvious entry points for additional roleplay.
4) Provides distinctions for "Legal" gear, "Restricted" gear, and "Forbidden" gear with respect to acquisitions.
5) Allows for higher degrees of success -- hits above the required mark in RAW are effectively discarded, while in the house rule each hit counts fully.
6) Brings Etiquette back into play as a necessary and commonly used skill even for non-Faces.
The cons:
1) Probably too calculationally intensive for some people.
2) This method probably shortens most acquisition times for Restricted gear, especially for magic gear and cyberware. A rating 6 power focus (Availability 30R) would have a base acquisition time of 15 weeks in the house rule, modified down by the number of hits. My 10-dice runner will probably get those in 3-7 weeks. That could easily take the same runner 10+ weeks in the standard rules. Forbidden items by RAW, however, seem to fall into the middle of the expected range of the house rule for the same dice pool. That may break down at some extreme cases, but I haven't tested those.